308 G. H. PARKER 



muscles in the polyp of Corymorpha: (1) the longitudinal muscle 

 of the stalk, (2) the circular muscle of the stalk, (3) the longi- 

 tudinal muscle of the proboscis, (4) the circular muscle of the 

 proboscis, (5) the longitudinal muscles of the proximal tentacles, 

 and (6) the longitudinal muscles of the distal tentacles. This 

 enumeration does not include the longitudinal muscles of the 

 peduncles of the fixed medusae nor those of the medusae them- 

 selves, whose activity, as Torrey ('07, p. 255) has pointed out, 

 implies the presence of at least a subumbrellar band. In gen- 

 eral the polyp of Corymorpha exhibits the arrangement of 

 muscles found in the typical hydrozoan, a longitudinal ecto- 

 dermic system and a circular entodermic one. The longitudinal 

 entodermic system claimed by Lipin ('09, p. 355) for Poly- 

 podium is associated in that hydrozoan with a curious inversion 

 of the germ layers that may lay this interpretation open to 

 question. 



The functions of the several muscles already enumerated for 

 Corymorpha may be studied best by beginning with those of 

 the stalk. When a fully expanded, quiescent Corymorpha is 

 vigorously stimulated mechanically, its stalk shortens to about 

 one-half its former length (Torrey, '04 a, p. 401) and at the same 

 time thickens. Thus an expanded polyp whose stalk measured 

 4.7 cm. in length on contraction had a length of only 2.5 cm. 

 In ten such instances the average contracted length was 57 per 

 cent of the average expanded length. 



If the hydranth is cut off from Corymorpha the contractil- 

 ity of the stalk remains essentially unaltered. Thus a stalk 

 without hydranth that had an expanded length of 4.2 cm. had 

 on full contraction a length of 2.3 cm. and in ten instances of 

 this kind the average contracted length was 55 per cent of the 

 average expanded length. Thus the contraction and expansion 

 of the stalk are quite independent of the hydranth. 



If the activity of the whole stalk is studied, the contraction 

 is seen to occur in only that part which is ordinarily above the 

 mud, the half centimeter or so of buried stalk being incapable 

 of longitudinal contraction. This portion is devoid of longitud- 

 inal muscle fibers and hence should be expected to be non- 



