ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



50, A, eg). The stomodaeum is slung up to the body-wall by mesenteries 

 showing the same characteristics — muscles (m), mesenterial filaments 

 («./), gonad — as in the Alcyonarians but these mesenteries show charac- 

 teristic differences in their arrangement. They are more numerous 

 and are distinguishable into different sets — primary mesenteries, which 

 at their inner edge are attached to the wall of the stomodaeum, and others 

 (secondary, tertiary, etc. — Figs. 49 and 50, s.m) much smaller, which 

 extend inwards only a short distance and do not reach the stomodaeum. 

 Of primary mesenteries the number is from twelve upwards. They 

 are arranged in couples and in each couple the muscular thickenings 



Fig. 50. 

 Transverse sections through a simple Sea-anemone (Peachia). A, Tlnrough stomodaeum ; 

 B, below stomodaeum. eg, Ciliated groove ; d, directive mesenteries ; ect, ectoderm ; end, endoderm ; 

 m, muscle ; m.f, mesenterial iilament ; s.m, secondai-y mesentery ; st, stomodaeum. The mesogloea 

 is indicated by a black line. 



face towards one another, except in the case of the directive mesen- 

 teries, the couple which support the ventral ciliated groove and the 

 couple directly opposite, which support the dorsal ciliated groove if 

 there is one. In the case of these directives the muscles are borne not 

 on the inner but on the outer surface, i.e. they face away from one 

 another (Fig. 50, d). 



The ordinary sea-anemone attaches itself temporarily, the attachment 

 being aided by cement secreted by the gland-cells of its base. While as a 

 rule this cement is imperceptible it may on the other hand form a dis- 

 tinct horny layer, as happens in Adamsia, an anemone which commonly 

 lives symbiotically on shells inhabited by Hermit Crabs. Finally in 

 a large subdivision of the Zoantharia the secreted mass, composed of 



