///. ANTIIOZOA. 



253 



the moseuteries of the mammals. Lower down, in some species, 

 the filaments become free and form long threads, acontia, rich in 

 nettle cells which are protruded for defence either through the 

 mouth or pores [cinclides) in the column. The gonads — only 

 exceptionally hermaphroditic — lie inside tlie mesenterial threads 

 as band-like folded thickenings (fig. 201, /*•'). They arise as in 

 the Scyphomedusse from the entoderm, but early migrate into the 



Fig. 201. 



Fig. 203 



FxQ oQl —Sections of Ceveus spinosus, showing complete and incomplete septa. 



.'/ acontia; b, mesenterial filament; c, septal stoma; g, tconarls; ft\ septa of tirst 



order with gonads; W^—h', incomplete septa of second to tourtli order; t'~i', 



corresponding tentacles. 

 Fig. 202. • ■■ " ' -" 



me. 



lU.ei WlLll f^Ullcl.\.l.^, I" •- 1 — ._ .^.**^.^. .^ .-^i 



"i'o'o'fFg^otion oTseptum of Echimrdsin UiherrMiitd. ek. ectoderm; en. entoderm; 

 le, "supporting layer; m/, septal muscle; ", ovary ; y, mesenterial filament. 



mosoglcea of the septum (fig. 202, o). The eggs, when ripe, 

 escape into the gastrovascular cavity by deliiscence. The young 

 leave the parent at various stages of development, sometimes as 

 plannhB (fig. 200, A), sometimes as young with tentacles. 



The muscles are very important, morphologically. Muscles 

 and nerves occur in both ectoderm and entoderm: but while the 

 nerves are best developed in the ectoderm, forming especially a 



