No. 3-] PODARKE OBSCURA VERRILL. 417 



certainty was that represented in PI. XXXVII, Fig. 23. I 

 believe that they become slightly larger in the later stages and 

 form a part of the general ectoderm of the umbrella. Once 

 and only once did I see an indication of a division in one of 

 these cells, idi.i.2.2.2.1. This I believe was abnormal. They 

 certainly do not become slime glands (excretory glands .'') in 

 Podarke, unless the small deeply staining cells scattered over 

 the surface have that function, for there are no such large 

 glands as Mead has described for Amphitrite. 



The anterior arms of the cross next divide meridionally. 

 (See the division begun in PI. XXXVII, Fig. 19, and com- 

 pleted in PI. XXXVII, Fig. 20.) At their next division a 

 number of small cells appear (PI. XXXVII, Fig. 22). Note 

 especially the small size of these cells and their deeply staining 

 nuclei. To avoid tedious description I have indicated by junc- 

 tion lines in PI. XXXVII, Fig. 22, the origin of many of these 

 cells, and have put their divisions in the table, p. 438. In PI. 

 XXXVII, Figs. 18-23, the outline of the cross is indicated 

 by the heavy line. 



Beyond the stage represented in PI. XXXVII, Fig, 23, I 

 have not attempted to carry the lineage of the anterior (ven- 

 tral) portion of the umbrella. The cross cells become inextri- 

 cably confused with the descendants of the intermediate group, 

 and, with possible exceptions, all contribute to the formation 

 of the ventral ectoderm. The exceptions are these. I believe 

 that some of the very small cells are pushed into the cleavage 

 cavity and finally absorbed. Immediately after they are formed 

 they sink below the surface, lying near the bottom of the rather 

 thick ectoderm. A little later dark bodies are seen lying inside 

 the segmentation cavity, and later still they touch the en- 

 toderm (see Text-Fig. 8, ecf). The point needs reinvesti- 

 gating before it can be considered absolutely proven, but 

 I believe the fate of the cells is as I have described. A 

 similar process occurs in Crepidula (No. 5, a), where, however, 

 the cells are thrown outside the body, and more recently Miss 

 Langenbeck (No. 20) has described, in Microdeutopus, cells 

 which are taken into the segmentation cavity. In Lepidonotus, 

 Mead (No. 22) states that the polar globules 'pass into the 



