Note 1) Declining Number of Priests

Ordinations of secular priests in the fifties:- 1952: 85 priests (Catholic Directory for 1953, p.444). 1953: 119 pr (C.D. 1954, p.465).  1954: 146 pr (CD 1955, p.474) . 1955: 119 pr.  (CD 1956, p.488).  1956: 146 pr. (CD 1957, p.492).
Average for those five years  123 per annum. NB in 1956 Southwark alone  ordained 26.
Ordinations of secular priests in 2002: 53 (CD 2003, p.924).   2003 : 36 (CD 2004, p.925.) 2004: 10 (CD 2005, p.888). Average (for 3 years) : 33.

Note 2) The Present Legislation

The rules contained in the Codes of Canon Law of 1983 and 1918, as well as the older Corpus Iuris Canonici, are traceable to the First and Second Lateran Councils of 1123 and 1139. Canon 7 of the former and Canon 6 of the latter formally prohibited marriage for those in major orders. (Source: Concilium Oecumenicorum Decreta, ed. J.Alberigo et al. Bologna 1972, pages 191, and 198)
The deliberations of those councils have not survived, but the motives underpinning the legislation can be discerned from the statements of contemporary high ranking ecclesiastics.
Cardinal Humbert (1054), commenting on the lives of Greek priests declared:- “Young husbands , just now exhausted from carnal lust,serve the altar. And immediately afterwards they again embrace their wiveswith hands that have been hallowed by the Immaculate Body of Christ.That is not the mark of the true faith,but an invention of satan.” (cited in U.Ranke-Heinemann, Eunuchs for the Kingdom of Heaven, London 1990, p.107.)
Pope Innocent III, addressing the Council of Clermont 1130,declared “ Since priests are supposed to be God’s temples , vessels of the Lord and sanctuaries of the Holy Spirit ....it offends their dignity to lie in the conjugal bed and live in impurity”. (Ranke-Heinemann, p.110).
The cause of this pessimism about sex is explained by Gabriel le Bras who showed that a significant number of canonists and theologians in the middle ages maintained that the conjugal act could never be performed without sin. He quotes XII century writers including Cardinal Robert Pullen, Pierre de Poitiers, Pope Innocent IIi, Pierre le Chantre, and Robert de Courson. (Dictionnaire de Theologie Catholique, art. Marriage, Volume IX, column 2177).
Professor C.H. Lawrence summarised the underlying attitudes which gave rise to the laws forbidding clerical marriage in an important article in the Clergy Review 1975, (Origins of Clerical Celibacy) from which the most important section is as follows (page 140):-“ For St. Jerome the cardinal exponent of celibacy for the Middle Ages, marriage is an evil, if a lesser one; this was because he held conjugal intercourse and the life of prayer to be incompatible: ‘The Apostle commands us to pray always ; it is best then not to be in the bondage of marriage, for as often as I render to my wife what I owe, I cannot pray. What kind of good is this, which prevents a man from prayer and  does not allow him to receive the Body of Christ?’  ‘The reason (for forbidding marriage to the clerks)  is priestly purity  'observes the canonist Gratian in the twelfth century ‘so that they may be free to devote themselves to prayer’.  To the canonists, marriage was simply a form of licensed incontinence, and as such, a serious lapse from Christian perfection. The married clerk is an anomaly, writes Ivo of Chartres, ‘for a general permission conceded to human frailty is one thing; but a life dedicated to the service of divine things ought to be different’.
The rule of celibacy was founded in fact, as much upon the denigration of marriage and mistrust of sexuality, as upon esteem for the evangelical counsels. The vileness of sexual intercourse and its inherent sinfulness was a recurrent theme in the ascetical literature of the Middle Ages.” 
Note 3) Vatican II - Order & celibacy, Presbyterorum Ordinis, section 16 , page 565 in “The Documents of Vatican II”, ed. Walter M. Abbott, New York 1966.
Sex is morally good, Gaudium et Spes, section 49, Abbott p. 253.

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Note 4) The Vatican’s Reasons for Retaining Mandatory Celibacy 
The encyclicals (Sacerdotalis Coelibatus of Paul VI,  and Pastores Dabo Vobis of John Paul II) do not offer theological reasons for maintaining the present discipline.  In 1994  The Cong -  regation for the Clergy issued a document entitled “Directory on the Life and Ministry of Priests”, in which a justification for the present law was based on the concept of cultic purity  (i.e. Incompatibility between the sacred and disease, corpses, and sex). The evidence is relegated to a footnote in section 59, (see CTS translation, London 1994). The citations from  synods, Church Fathers and Popes are as follows:-Council of Nicaea 325 AD:-The great synod totally forbids that a bishop or priest or anyone else in the clergy should be allowed to have a woman who is a spiritual partner (Gk. suneiskaton) in the house unless perhaps it be his mother, sister, aunt or those persons who are above suspicion.
Council of Elvira (shortly after 300 AD), Canon 27:-  A bishop or any other cleric may have with him only a sister or a daughter who is a virgin dedicated to God ; it is our decision that he should never have a stranger (extraneam). Canon 33:- It pleased the synod completely to prohibit bishops, priests, deacons and all clergy serving in the ministry to abstain themselves from their wives and not to beget children: whoever should do this shall be removed from the ranks of the clergy. (N.B. This is contradictory, cf. explanation in M.M.Winter, Misguided Morality, p. 108).
Pope Damasus, “Ad Gallos Episcopos” c.374 AD, Chapter 3 “This is established in the first place concerning bishops, priests, and deacons, who of necessity must be present at the divine sacrifices, by whose hands the grace of baptism is conferred and the body of Christ is consecrated, they are compelled to be absolutely chaste, not only by our authority but also by the Holy Scripture and the Fathers too command them to observe bodily continence ...those who offered the sacrifices in the Temple remained in the Temple of a whole years, simply in virtue of their turn of duty, so that they should be clean, hardly knowing their homes.....If intercourse is a pollution, then indeed a priest must stand ready for the heavenly duty since he is to intercede for the sins of others, lest he should be found unworthy... and would the priest or deacon dare to take part, being subject to the behaviour of animals.”
Pope Siricius: Letter to Himerius Bishop of Tarragona (385 AD) Section 9 :-
‘Be holy, because I the Lord your God am holy’. (Lev. 20:7) Why were the priests commanded to dwell in the temple, far from their homes in the year of their tour of duty? Clearly it was for this reason, that they should not have carnal intercourse with their wives so that with conscience gleaming with integrity, they could offer an acceptable gift to God.  Priests and deacons are constrained by a binding law of continence...all priests and Levites, we are bound by an indissoluble law, that from the day of our ordination we are constrained  by sobriety and modesty of heart and body, so that we may please God in all things in the sacrifices which we offer daily.
Pope Siricius, Letter of 386 AD, chapter 9: “We consider that priests and Levites should not have intercourse with their wives because in the ministry , the minsiters are occupied with obligations which occur every day.”  The letter ends with a list of canons, the fourth of which declares :- “Bishops priests and deacons should abstain from their wives”.
Council of Carthage, AD 390, Canon 2:- “Bishops priests and levites must abstain from (conjugal relations with) their wives.
Council of  Carthage, AD 401, Canon 4 :- “Bishops priests and deacons  shall not live with their wives; if they do so they must withdraw from their functions. The other clerics will not be held to continence.”
Council of Telepte, c. AD 418, Canon 9 :- “We wish to recommend that which is worthy, modest, and honest, namely that priests and levites should not have intercourse with their wives because they are occupied by the daily demands of the service in the ministry”.
Pope Innocent I (402 - 417) Letter 6 :- “Priests whose ordinary occupation is to pray and to offer sacrifice, must always abstain from this kind of intimacy. If he should be contaminated by carnal concupiscence  how would he presume to take up the duty of sacrifice?”.
Pope Leo the Great (440 - 461), Letter 167 :-“The law of continence is the same for ministers of the altar, be they bishops or priests. When they were laymen or lectors it was lawful for them to contract marriage, and they were able to beget children. But when they were promoted to the aforementioned ranks, that which had been licit was not longer licit.”
Council of Neocaesarea (between 314 and 325) Canon 1 :- “If a priest contracts marriage, he will be excluded from the ranks of the clergy: if he should be guilty of adultery or fornication he will be excommunicated and must submit to penance”.
Eusebius of Caesarea, in his Demonstratio Evangelica (before 325 AD) commenting on I Timothy 3:2, wrote :- “Those who have been consecrated and who are occupied with the divine service are recommended to refrain from intercourse with their wives”.
Epiphanius, in his work Against All Heresies (end of fourth century) Book II, Volume 1,chapter 4:- wrote that remarriage after the death of a wife was permissible because of human frailty, but not for a priest “who would  have refrained from intercourse with one wife”.
Epiphanius, Expositio Fidei, (Book III, Volume 2, chapter 21), in the context of forbidding a second marriage to a priest, “ It is customary to elevate to the priesthood those who refrain from their wives, or who are living as widowers after one marriage”.
Council in Trullo, 692 AD, Canon 13:- “ In the Roman church those who wish to receive the diaconate or priesthood promise to have no further intercourse with their wives. As for us who keep the Apostolic Canons, we permit the continuation of the conjugal life. Whoever wishes to dissolve such unions will be deposed, and the cleric, who under pretext of religion abandons his wife, will be excommunicated. The subdecaons, deacons, and priests must always refrain from sexual intercourse with their wives during the times when they exercise their sacred functions, for the council of Carthage had ordained that whoever serves in the sanctuary must be pure”.
(NB It is a surprisingly meagre amount of evidence in view of the mass of patristic writings of that period and the numerous Councils, both local and general. Amplification of these bald statements, evaluating them and setting them in their historical and theological context can be found in the book “Misguided Morality” by M.M.Winter, pages 91-97 & 107 - 114.)

Note 5) Vatican II,  Lumen Gentium, sections 22 - 24, (Abbott pp 42 - 48), Christus Dominus, sections 4 - 6, (Abbott pp. 398 - 400).