The germ-cells. 635 



pleure would be free of them ^). The majority of them certainly lie 

 higher than, that is, dorsad of, the level of the gut. There is, however, 

 one place on the splanchnopleure, which is very frequently occupied 

 by one or two such germ-cells. This is the ventral side of the sub- 

 intestinal vein or veins (Figs. 16 and 21). A single one, or some- 

 times two such germ-cells side by side are met with so often, that 

 one is bound to notice it. Comparing such cells and their position 

 with the normally placed germ-cells and their location in the so-called 

 "germinal ridge" and just outside the posterior cardinal sinus, one is 

 struck by the similarity. In both each germ-cell stands within a 

 more or less regular epithelium, a portion of the splanchnopleure, and 

 immediately to the inner side a nutrient blood-stream courses by, in 

 the one case the posterior cardinal, in the other the subintestinal 

 vein 2). 



On the somatopleure the "lost germ-cells" are much rarer, and 

 this is the case more especially in embryos of 18 — 20 mm and up- 

 wards. As far as can be made out from my notes there are less 

 than a dozen in this situation in No. 454. In young embryos of 

 10 mm and under they are far more numerous. Sometimes one is 

 found on the somatopleure right opposite the subintestinal vein, i. e., 

 on the extreme ventral portion of the somatopleure (Fig. 11). Nine 

 sections further on than this there was another in exactly the same 

 position. This is a little fact of possibly greater significance than is 

 apparent on the surface. 



When, lastly, the body-cavity itself is mentioned as a place, in 

 which such free and uncontrolled germ-cells are met with, the list of 

 their occurrence in the present embryo has been about exhausted. 

 Those found in the body-cavity of No. 454 are all depicted in Figs. 38 

 to 48. Here, except that shown in Fig. 40, the coelomic germ-cells 

 are obviously in a degenerate condition. But the one depicted in 

 Fig. 40 is also in degeneration, for Flemming has pointed out, that 

 diminution in size is one of the most characteristic features of the 

 degeneration of germ-cells ('85, p. 237). 



1) The like is true of Rabl's form, Pristiurus, at certain periods, 

 as may be demonstrated by figures on a subsequent occasion. 



2) It is an interesting question, whether the posterior cardinals 

 arose in connection with the lodging of the germ-cells, or whether the 

 latter attached themselves to the already existing veins. The genital 

 sinuses of later periods appear to be nothing more than local dilatations 

 of the cardinals. 



Zool. Jahrb. XVI. Abth. f. Morph. ^2 



