REPRODUCTIVE ENDOCRINOLOGY IN BIRDS 



1147 



1949; Fraps, 1955b). After ovulation, the 

 yolk (secondary oocyte) either falls into 

 the ovarian pocket and is subsequently en- 

 gulfed by the funnel of the oviduct, or it 

 may immediately fall into the funnel when 

 the latter is partly covering the mature fol- 

 licle. 



The yolk is moved down the oviduct 

 by peristaltic movements, and, during this 

 passage, albumen is deposited around it. 

 The albumen has been accumulated in the 

 glands of the oviduct during the period 

 between successive yolks coming down the 

 oviduct (Conrad and Scott, 1942). On pas- 

 sage of the yolk, the albumen is hydrated 

 and transferred to the lumen of the oviduct 

 (Smith, Hoover, Nordstrom and Winget, 

 1957). Part of the albumen accumulation 

 in the magnum of the oviduct seems to occur 

 continuously whereas another part is se- 

 creted in larger quantities when ovulation 

 is imminent (Smith, Court and Martin, 

 1959) . The egg is transferred from magnum 

 to isthmus where the membranes are formed 

 around the albumen. After this stage is com- 

 pleted, the egg is moved into the shell gland 

 where the thin albumen is added through the 

 egg membranes to give the egg its plumped 

 appearance. This process takes 3 to 5 hours, 

 and during this process shell deposition also 

 starts (Bradfield, 1951). Of the egg-shell 

 calcium, 60 to 75 per cent comes directly 

 from the food (Driggers and Comar, 1949). 

 These workers found that an egg laid within 

 10 minutes after an oral dose of Ca^^ con- 

 tained radioactive calcium, evidence for the 

 very rapid transfer as w'ell as for the con- 

 tinuous deposition of calcium while the egg 

 is in the oviduct. In some breeds of chickens 

 porphyrin is deposited on the shell to give 

 it a brown color. According to recent in 

 vitro studies, the porphyrin is synthesized 

 from 8-amino-levulinic acid by the shell 

 gland tissue (Polin, 1957). In vitro no dif- 

 ference was found between the amount of 

 porphyrin synthesized by tissue from breeds 

 laying white-shelled eggs and breeds laying 

 brown-shelled eggs. Polin (1957) suggested 

 that white shells are white because of a lack 

 of 8-amino-levulinic acid in the tissues, and 

 not because of a lack of enzyme systems for 

 the synthesis of porphyrin from S-amino- 

 levulinic acid. During the sojourn in the 



shell gland, the egg is rotated on its longi- 

 tudinal axis (Conrad and Phillips, 1938), 

 which causes some of the mucin material in 

 the albumen to form strands. The formation 

 of these twisted strands squeezes out some 

 of the water to form the inner thin albumen 

 (Conrad and Phillips, 1938). Shell forma- 

 tion continues until complete oviposition 

 occurs. 



The physiologic mechanisms which ini- 

 tiate oviposition are not well understood. 

 A variety of treatments, including injection 

 of posterior pituitary hormone, vasopressin, 

 and oxytocin can cause premature oviposi- 

 tion. Soft-shelled eggs can be obtained in 

 this manner (Burrows and Byerly, 1942; 

 Burrows and Fraps, 1942). It is known that 

 the posterior pituitary glands of chickens 

 contain vasopressin and oxytocin (de 

 Lawder, Tarr and Gelling, 1934; Heller, 

 1950) ; however, posterior pituitary removal 

 does not interfere with either ovulation or 

 oviposition, although it does result in dia- 

 betes insipidus, thus indicating that the an- 

 tidiuretic hormone is absent (Shirley and 

 Nalbandov, 1956a). An analogous situation 

 is observed in rats from which the posterior 

 pituitary is removed. Such rats are unable 

 to nurse their young because the milk ejec- 

 tion cannot occur in the absence of the pos- 

 terior pituitary hormones. After a subse- 

 quent pregnancy these rats will deliver the 

 young normally indicating normal release 

 of oxytocin. The dams can nurse their young 

 normally in spite of diabetes insipidus (Ben- 

 son and Cowie, 1956). These data indicate 

 that oxytocin can be released from the re- 

 generated stalk, where the NSM from the 

 hypothalamic nuclei has accumulated. This 

 release occurs in response to a reflex stimu- 

 lus, but for some reason, the antidiuretic 

 hormone is not released. It is entirely pos- 

 sible, therefore, that the posterior pituitary 

 hormones, or rather the NSM from the hypo- 

 thalamus, are involved in oviposition, but 

 this is a matter of speculation. 



In addition to posterior pituitary hor- 

 mones, acetylcholine injections cause pre- 

 mature expulsion of the egg, and ephedrine 

 delays oviposition (Weiss and Sturkie, 

 1952). As mentioned, the ruptured follicle 

 and the largest maturing follicle may secrete 

 a hormone involved in expulsion of the egg, 



