VI.] THE WOLFFIAN BODY. 161 



part in the formation of the ovary. Soon after its appearance, 

 the intermediate cell-mass increases in size and beoins to 

 grow outwards into the pleuroperitoneal cavity, as a rounded 

 projection which lies with its upper surface towards the 

 somatopleure, and its lower surface towards the splanchno- 

 pleure, but is in either case separated from these layers 

 by a narrow chink. The Wolffian duct (Fig. 44, Wd, 47, 

 Wd) travels down, and finally before the end of the third 

 day is found in the upper part of this projection, near that 

 face of it which is turned towards the somatopleure. 



At, or before, the fourth day, when the duct occupies 

 this new position, the Wolffian body begins to be formed in 

 the midst of the intermediate cell-mass. 



The structure of the fully developed Wolffian body is 

 fundamentally similar to that of the permanent kidneys, and 

 consists essentially of convoluted tubules, commenciug in 

 Malpighian bodies with vascular glomeruli, and opening 

 into the duct. It is formed as follows. 



From the anterior portion of each duct and on its inner 

 side, diverticula are given out at right angles. These 

 gradually lengthen, and becoming twisted form the tubules, 

 while the glomeruli of the Malpighian corpuscles seem to be 

 derived from cells of the intermediate mass, which also gives 

 rise to the vascular networks round the tubules. 



The tubules, which from their contorted course are in 

 sections (Figs. 47, 51) seen cut at various angles, possess 

 an epithelium which is thicker than that of the Wolffian 

 duct. From this difference it is generally easy to distin- 

 guish the sections of the tubules from those of the duct. 

 The glomeruli of the Malpighian bodies are in sections of 

 hardened embryos usually rilled with blood-corpuscles. 



In the above statements we have followed "Waldeyer (Eierstock und Ei), but 

 it ought to be mentioned that the majority of earlier observers have believed 

 that the tubules arise independently in the mesoblast, and only at a later period 

 become connected with the duct. The sections which Waldeyer has drawn 

 seem however strongly to support the view which he has brought forward ; 

 our own sections also confirm it, and we have noticed that even before the 

 formation of the tubules, the Wolffian duct exhibits great variations in diameter, 

 being in some cases crescent-shaped in section, in others round ; this seems 

 clearly to indicate the giving off of diverticula. W T aldever's observations have 

 moreover been since confirmed by other observers. 



The Wolffian body, as distinct from the duct, reaches 

 from about the level of the fifth protovertebra to beyond the 



E. 11 



