III. ANTHOZOA. 



253 



the mesenteries 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 the mesenterial threads 

 as band-like folded thickenings (fig. 201, 7^ 3 ). They arise as in 

 the Scyphomedusae from the entoderm, but early migrate into the 



FIG. 201. 



FIG. 202 



FIG. 201. Sections of Cereus spmostts, showing complete and incomplete septa. 



u, acontia; 6, mesenterial filament; c, septal stoma; g, gonads; ft 1 , septa of first 



order with gonads; /i 2 /i 4 , incomplete septa of second to fourth order; t 1 * 4 , 



corresponding tentacles. 

 FIG. 202. Section of septum of Edioardsia tuberculnta. ek, ectoderm; en, entoderm; 



me, supporting layer; mf, septal muscle; o, ovary ; u, mesenterial filament. 



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

 escape into the gastrovascular cavity by dehiscence. The young 

 leave the parent at various stages of development, sometimes as 

 planulae (fig. 206, 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 



