i050 



EMBRYOLOGY. 



Fig. 585. 



and bodies of Oken — are glandular in structure, and extend in front of the vertebral 

 column from the heart to the pelvis. They are composed of small transverse 

 canals, filled with a whitish fluid, which enter a common excretory duct that lies 

 parallel to the spine, and opens inferiorly into that portion of the allantois which 

 becomes the bladder. 



The Wolffian bodies are placed behind the peritoneum, and are attached by 

 two serous folds : an anterior — the diaphragmatic ligament — and a posterior — the 

 lumbar ligament of the corpora Wolffiana. The organs furnish a liquid analogous 

 to the urine ; though it is not long before their secretion undergoes great modi- 

 fications ; indeed, these bodies soon atrophy,, and disappear more or less rapidly, 

 according to species. One portion serves for the development of the genital 

 organs ; the other gives rise to organs the signification of which is unknown — 

 such as the organ of Rosenmiiller — which is very developed in the Mare, and the 

 canals of Gaertner, visible in the Cow and Rabbit (Mare and Pig). 



A. Urinary Organs. — We have seen above how the allantois is derived 

 from the blastodermic lamina ; it has now to be stated that the bladder is derived 

 from the allantois. This reservoir is the result of the dilatation of the abdominal 

 portion of the allantois. During foetal life, the bladder is extended, by the 

 urachus, to the umbilical ring ; but after birth the urachus is obliterated, and 

 the bladder is withdrawn into the pelvic cavity. Hereafter we shall study the 

 urethra. 



The kidneys appear a long time after the Wolffian bodies, in the shape of two 

 blind pouches constituted by a pushing back of the wall 

 of the excretory duct of that body. These little cuJs-de- 

 sac ramify, and are afterwards replaced by solid buds, in 

 the interior of uhich are developed the uriniferous tubes 

 and Malpighian bodies. According to certain observers, 

 the kidneys subsequently communicate with the ureters, 

 which are developed separately in the middle layer of 

 the blastoderm (for further details, see Book IV., p. 573). 

 (In the female, the Wolffian bodies do not entirely 

 disappear ; the canals of Gaertner and the bodies of 

 Rosenmiiller, situated in the broad ligaments, between 

 the ovaries and Fallopian tubes, are their remains in 

 adult life ; traces of them are also found in the male, near 

 the head of the epididymis, where they constitute the vasa 

 aberrayis of the testicles. The supra-renal capsules are 

 very large in the Equine foetus, being nearly one-half the 

 size of the kidneys.) 



B. Genital Organs. — The genital apparatus of the 

 male and female are at first very much alike ; indeed, 

 during a certain period it is impossible to distinguish 

 the sexes ; so that some authorities have proposed to term 

 this period of development the " indifferent state of the genital organs." Later, 

 the sexes are defined ; and this period of development may be studied in the 

 internal and external organs. 



1. Indifferent state of the internal genital organs. — Towards the sixth week, 

 there is observed on the lower face, and near the inner border of the Wolffian 

 bodies, a little white cord, which increases in volume and maintains almost the 

 same position. This new organ is the genital gland, which is attached to the 



STATE OF THE GENITO- 

 URINARY APPARATUS IN 

 THE EARLY EMBRYO OF 

 THE BIRD 



a, Corpora Wolffiana ; 6, 6, 

 their excretory ducts; 

 c, kidneys ; d, ureter ; 

 €, e, testes. 



