VII.] THE WOLFFIAN BODY. 213 



with the general folding in of the body, cause it to 

 appear to change its place and travel downwards (p. 

 193). While the shifting is going on, the cells lining 

 the upper end of the pleuroperitoneal cavity (the kind 

 of bay which, as seen in sections, is formed by the diver- 

 gence of the somatopleure and splanchnopleure) become 

 columnar, and constitute a distinct epithelium. This 

 epithelium, which is clearly shewQ in Fig. 64, and is 

 also indicated in Fig. 65, is often called the germinal 

 epithelium, because some of its cells subsequently take 

 part in the formation of the ovary. Soon after the ap- 

 pearance of the germinal epithelium, the intermediate 

 cell-mass increases in size and begins to grow outwards 

 into the pleuroperitoneal cavity, as a rounded projection 

 w^hich lies with its dorsal surface towards the somato- 

 pleure, and its ventral surface towards the splanchno- 

 pleure, but is in either case separated from these layers 

 by a narrow chink. The Wolffian duct (Figs. 65, 68, 

 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. 



The tubules of the anterior part of the Wolffian 

 body have by the end of the fourth day almost entirely 

 disappeared ; but the tubules of that part of the Wolf- 

 fian body which is found behind the 16th segment 

 undergo a further development. 



Each increases in size especially that portion which 

 proceeds from the Malpighian body and is known as the 

 coiled tubulus (region No. 3, see p. 193). This becomes 

 much elongated and twisted. As a consequence of this 

 increase in size the intermediate cell-mass comes to 

 project more and more into the pleuroperitoneal cavity. 



