CHESTER. — STRUCTURE OF PSEUDOPLEX.VUR.V CKASSV. 7G1 



distance on to the base of the tentacles. In the small canals (as in 

 Fig. 50, mif'nm.) they are generall\' circular. (3) The stomodaeum 

 system. Endodermal muscles are feebly developed in the stomo- 

 daeum, Avhere they run circularly (Plate 3, Fig. 30). At the oral end, 

 and to a less extent at the coelenteric end, they are larger and more 

 numerous, but hanlly enough so to be termed sphincters. (4) The 

 mesentery system. These are, of course, endodermal. The longitu- 

 dinal muscles, on the ventral side of the mesogloea (Fig. 33. Com- 

 pare Plate 1, Figs. 2-4), are independent of the epithelium. The 

 folding of the mesogloea, which in cross sections appears branched, 

 is such as to accommodate a large number of fibers without a cor- 

 responding increase in the width of the mesenteries. Transverse 

 muscles are found on both sides of the mesentery (Fig. 33) ; they are 

 comparatiA'cly few and are an-anged in a single sheet, i. e., without 

 foldings. 



Physiologically the muscles may be divided into, first, the longi- 

 tudinal muscles of the ectoderm of the tentacle and disk and the 

 strong longitudinal endodermal muscles of the mesenteries; secondly, 

 the circular endodermal muscles of the polyp wall and canals together 

 with the transverse muscles of the mesenteries. 



The nerves can hardly be said to be arranged in a system, as they 

 surely are in colonies of more active alcyonarians. Sense cells are 

 found, particularly in connection with the nettle batteries, and gang- ' 

 lion cells are scattered in the deeper layer of the ectoderm of both 

 column and stomodaeum. But there is no conspicuous ner\e layer, 

 such as that foimd by Kassianow (:08) in Alcyonium. 



The weakness of the nerve layer accords with the slowness of the 

 polyps in contracting. These do not respond to touch as quickly as 

 many other related forms living near them, such, for example, as 

 Euniceopsis, Plexaura and Gorgonia. The tentacles show no response 

 to a single light touch, but a sharp touch, or one repeated, gi\-es a 

 reaction, which is always toward the mouth, as is to be expected from 

 the fact that the muscles are limited to the oral side. The response 

 of one tentacle, however, is accompanied by a response of the other 

 seven. The disk and column respond to touch, and the column 

 responds more quickly and vigorously near its base than elsewhere. 

 But the coenosarc l)etween the polyps is the most sensitive part of 

 the colony to touch. When this region is stimulated, the adjacent 

 polyps respond by a slow contraction toward the le^•el of the coeno- 

 sarc; the response, however, is more certain than when the column 

 is touched. There seems to be no nerve system connecting polyps 



