220 



Ca-LENTERATA 



... inf 



the rt'sopliagus, there may he others which do not reach the esophagus 

 and liehinij;iiig to secondary, tertiary or other series (lig. 104). 



The septa support a numl)er of important organs: tire mesenterial 

 hhimcnts, gonatls, and muscles. The iiwsciiteridl Jilaiiuiils are thick 

 strands of epithelium, rich in glands and nettle cells, fastened like a hem 

 on the edge of the septa. Since they are much longer than the peristomial- 



pedal length of the septa, they cause 

 these latter to wrinkle and fold, thus 

 strikingly resembling the mesenteiies 

 of the mammals. They en-\-elope the 

 food and press it in, thus aiding the 

 succeeding intracellular digestion. 

 Lower down, in some species, the 

 lilaments become free and form long 

 tlireads, acoiilia, rich in nettle cells 

 which are protruded for defence, 

 either through the moutli or pores 

 (cincliih's) in the column. The gonads 

 — only exceptionally hermaphroditic 

 — lie bcsitle the mesenterial tlrreads 

 as thickenings of the septum (lig. 

 192, g). The germ cells arise from 

 the entoderm, but early migrate into 

 tlie mesoglo-a of the septum (1Q3, 0). 

 The eggs, when ripe, escapie into the 

 gastrovascular cavity. The young 

 leave the parent at various stages of 

 development, sometimes as planukc 

 (lig. 107, A), sometimes as young with 

 tentacles. 



The muscles are ■WM-y important, 

 morphologically. Muscles anil nerves 

 occur in lioth ectoderm and entoderm; but while the nerves are best 

 developed in the ectoderm, especially around the mouth, and extend 

 into the mesgolcea, the muscles of the ectoderm are weakly developed 

 and are mostly confined to the peristome and the tentacles. The ento- 

 dermal musculature is much stronger, just outside of the tentacles is 

 usually a strong circular (sphincter) muscle (/») which can close in the 

 top of the column o\-er the peristome. The septa also bear muscles, 

 transverse on one side, longitudinal on the otlier, the hitter producing 

 ridges on die septa (hg. 193). 



'lie 



ck 



Fic. 193. — Seclion of soiilum of 

 Eihi'urdsiu tubcrciilala. ck, ccloilcnn; 

 en, enlO(ierm; nic, sup]Kirtln;; la\-i.'r; 

 mf, septal muscle; 0, ovary; i\ mesen- 

 terial iilament. 



