634 JOHN BEARD, 



In the sequel it will be difficult to put a limit to the extension 

 of "lost germ-cells" within the embryo. Even in the present embryo 

 No. 454 within the genital region of the body, i. e., over the trunk 

 from a point some little distance posterior to the commencement of 

 the nephridia and as far back as the cloaca, they may occur almost 

 anywhere ventrad of the notochord. 



With Balfour I have met them near the nephridia, within these, 

 or in, or on, the epithelium to their outer sides. Like Rückert and 

 Rabl I recognise their occasional presence in the myotomes. But 

 neither the number of those within the myotomes, nor of those in or 

 about the nephridia, in other words, not the whole of those within 

 the segmented portion of the mesoblast of this embryo — or for the 

 matter of that in any other of my embryos of R. batis — is suf- 

 ficiently large to allow of the statement, that any considerable portion 

 of the germ-cells is segmental in arrangement. 



In the segmented mesoblast of embryo No. 454 the number of 

 germ-cells is very small, only 2 are specially noted in my list as oc- 

 curring in this region. It may be added, that the number is larger 

 in younger embryos. 



Of vastly greater importance as the seat of germ-cells is the 

 splanchnopleure. This is true of no restricted portion of it; but, in 

 addition to the "germinal ridges", it applies to the whole of the peri- 

 toneum of the mesentery and to that covering the gut. As shown in 

 table 1, there are no fewer than 110 germ-cells at various points on 

 the mesentery, and this number is out of a total of 512. In addition 

 to these there are also some 12 or so within the mesentery at so 

 considerable a distance from the "germinal ridges", that they cannot 

 be said to have any connection with them ^). 



No point on the mesentery, or on the peritoneum of the gut, is 

 exempted from the attentions of such germ-cells. Were one to draw 

 a schematic transverse section of the embryo to scale, and then to 

 mark out on the mesentery and peritoneum of the gut the points, at 

 which in various sections the various germ-cells in question were placed, 

 it appears certain, that in the diagram no single bit of the splauchuo- 



found in many specimens taken directly from the sea- weed (Halidrys 

 siliquosa) on the shore at low water, and preserved the same evening, 

 or next morning. That is to say, these embryos were in no sense 

 "artificially reared", like those of Baja and Pristiurus. 



1) Germ-cells within the splanchnopleure and within or near the 

 region of these ridges are classified as normal. 



