404 PERCY SLADEN TRUST EXPEDITION 



Larv^ with Twelve Mesenteries. 



10. Larva I. (PI. 24, fig. 20.) 



The larva is opaque-white, much flattened orally and aborally ; its length is '5 mm. 

 and diameter 75 mm. There are 12 radiating grooves on the peristome. The stomodgeum 

 is short and without ridges. 



Of the mesenteries 8 are complete and 4 incomplete but their muscles are so 

 little developed that their arrangement is uncertain. Filaments are only produced for 

 any distance on one lateral and one directive mesentery, and on these they have very 

 large nematocysts. 



The ectoderm of the column and stomodseum is thick and vacuolated; nematocysts 

 are comparatively few but of two kinds, small with a close spiral thread and large with 

 a loose spiral thread ; granular and mucous gland cells occur. The endoderm is compact, 

 with numerous zooxanthellse ; between the mesenteries it is produced into the coelenteron 

 and more vacuolated. 



Loc. South of Saya de Malha Bank, surface. 



11. Larva II. (PL 24, fig. 21.) 



The larva is opaque-white, irregularly cylindrical, narrowing aborally ; its length is 

 •66 mm. and diameter '5 mm. There are no grooves on the peristome. The stomodseum 

 is very short. 



All the mesenteries reach the aboral end, but, as the stomodaeum is excentric and as 

 the parts are not clearly defined on the side where the mesenterial chambers are small, it 

 is impossible to see their arrangement. One mesentery has a much greater radial extent 

 than the others and is the only one with a filament. The latter has large spiral 

 nematocysts, and on the free edges of two other mesenteries similar nematocysts are 

 found near their aboral ends. 



The ectoderm of the column and stomodeeum is similar to that of the last larva, 

 but it is more compact and only the smaller nematocysts ai-e found. The endoderm is 

 likewise similar ; zooxanthellse are numerous and smaller, elongated, homogeneously 

 staining bodies, pointed at each end and quadrilateral in section. 



Loc. South of Saya de Malha Bank, surface. 



12. Larva III. (PI. 24, fig. 22.) 



The larva is translucent, flattened orally and aborally and shrunken ; its length 

 is 1 mm. and diameter 1-66 mm. The stomodaeum is long but of small diameter. 



Of the mesenteries 8 are complete and 4 incomplete, but filaments are only found 

 on the 4 complete laterals ; the epithelium of the enterostome is continued on to the 

 sides of these and then passes to form their filaments, spreading out over their greatly 

 expanded edges (fig. 23). Beneath the latter occur spherical bodies, homogeneous 

 parietally and vacuolated within, and some large nuclei are found near. What these 

 bodies are is uncertain, but they occupy to some degree the position of reproductive 

 cells. Muscles are not distinguishable. 



