TROCHOPHORE (W HYDROIDES UXCINATUS (EUrOMATUS). 577 



strands in Polygordius are in many ways comparable to the 

 lateral portions of the larval or ectomesoblast of Thalassema 

 and Annelids. The condition in Polygordius, where the 

 ectomesoblast arises and. becomes functional so much earlier 

 than the ccelomesoblast, shows that the head-kidney strands 

 do not form from the bands, and this point is borne out hy 

 the cell-liueage as worked out by Woltereck (52). In 

 Eupomatus the formation of the ccelomesoblast follows so 



Text-figs. 25 and 20. 



oes 



Tnesc, 



(xn. 



Sections througli the anal ends of early larva? of Eupomatus. 

 (iti. Anns, aii.v. Anal vesicle. r(p.m. Ccelomesoblast. hlc. 

 Head kidney, ect. Ectoderm, g. Gut. ces. CEsopliagns. 



closely on that of the ectomesoblast that this difference is not 

 so nmrked. 



To sum up: the ccelomesoblast in Eupomatus is not 

 recognisable until a relatively late stage in gastrulation, 

 and. the cells described by Hatschek and Soulier as the 

 mesoderm cells are probably portions of the larval or ecto- 

 mesoblast. At the time the ectomesoblast is represented, by 

 two cells on each side of the mouth, the ccelomesoblast is 

 represented by a cell in either side of the gut-wall above 



