THE \TOLFITIAX BODIES. 



777 



oesophagus. They are united at the anterior part of their 

 circumference ; and here a pedicle is formed which becomes 

 elongated into the trachea (see fig. 243, A, B). Soon after- 

 wards, the lung is seen to consist of a mass of csecal tubes 

 issuing from the branches of the trachea. (Fig. 243, c). 

 The diaphragm is early developed. 



The Wolffian Bodies, Urinary Apparatus, and 

 Sexual Organs. 



The Wolffian bodies are organs peculiar to the em- 

 bryonic state, and may be regarded as temporary, rather 

 than ntdimental, kidneys ; for although they seem to dis- 

 charge the functions of these latter organs, they are not 

 developed into them. They probably bear the same relation 

 to the persistent kidneys that the branchiae of Amphibia 

 do to the lungs which succeed them. 



In Mammalia, the Wolffian bodies (fig. 244, W.) are bean- 

 shaped, and are composed of transverse csecal canals, united 

 by an excretory duct (w) which leads from the lower ex- 

 tremity of the organ to the sinus-urogenitalis of the foetus 

 (fig. 244, ug). The kidneys (r) and supra-renal capsules (sr) 

 are developed behind them. Their size is at first so great 

 that they entirely conceal the kidneys ; but in proportion 

 as the latter bodies increase in size, they grow relatively 

 smaller, and come to be placed more inferiorly. At length, 

 towards the end of foetal life, only an atrophied remnant 

 of them is left. Their ducts, in the male, are ultimately 

 developed to form the vas deferens and ejaculatory duct of 

 each side ; the vesiculse seminales forming diverticula from 

 their lower part. In the female, the ducts of the Wolffian 

 bodies disappear. 



The testicles or ovaries are formed independently 

 at the internal excavated border of these organs ; and at 

 first it is not possible to say which of them the testicle- 

 or ovary the new formation is to become. Gradually, 

 however, the special characters, belonging to one of 



