56 



WHEELER. 



[Vol. VIII. 



surface. The resemblance of the " micropyle " to the indusium 

 is apparent at a glance {cf. Fig. 2, PI. I). I have followed the 

 organ in Amirida through the later stages by means of sections 

 and find that it persists for some time as a simple thickening 

 of the blastoderm, still connected with the peculiar striated 

 membrane which stands away from the surface of the blasto- 

 derm at all other points. Finally, when the embryo has 

 become flexed dorsoventrally and the body-walls are closed, 

 it sinks into the yolk and is absorbed. 



, A.O. 



Fig. V. 



Median section of the egg of Aniirida maritima. 



blastoderm. 



d.o., "micropyle"; bid.. 



Although much simpler in its structure, I do not hesitate 

 to homologize this " micropylar " organ in Amirida and the 

 Poduridae in general with the indusium of XipJiidmm. A pos- 

 sible objection to this homology, on the ground that the indu- 

 sium arises on the ventral face of the &^g, while the Podurid 

 "micropyle" is dorsal, has little weight, since the organ bears 

 in either case the same relation to the head of the embryo. 

 Provided, therefore, the egg of Amirida were to acquire yolk 



