96 



HYDR0Z0A. 



5. Order 4 : Calycophoridae. — The members 

 of the next order, CalycophoridcE, appear, at first 

 sight, very dissimilar in aspect to the fixed Hy- 

 drozoa, which, nevertheless, in all essential cha- 

 racteristics, they closely resemble, Diphyes, the 

 type of the group, presents a delicate filiform 

 coenosarc, to the proximal extremity of which are 

 attached two large, firm, mitrate, nectocalyces 

 (fig. 20, a). To these appendages, which differ 

 slightly in form, the distinctive terms of i proxi- 

 mal ' and ' distal ' have been assigned. The former, 

 as its name imports, precisely terminal in position, 

 is furnished with a conical cavity running parallel 

 with, but distinct from, its nectosac. Into this 

 cavity is fitted the apex of the distal nectocalyx, 

 along the inner surface of which it prolongs itself 

 as a lengthened groove, with its sides arched over 

 in such a manner as to form a more or less per- 

 fectly closed canal. The coenosarc, with its nu- 

 merous appendages, freely glides up and down the 

 peculiar chamber, or ' hydroecium,' thus produced, 

 into which it can, upon occasion, be completely 

 retracted. The coenosarc itself dilates slightly 

 towards its proximal extremity into a small ciliated 

 chamber, which, narrowing above, becomes con- 

 tinuous with a sac of larger size, termed the ' soma- 

 tocyst.' This, too, is ciliated, its cavity appearing 

 in most cases almost obliterated through excessive 

 vacuolation of the endoderm. The somatocyst 

 is firmly embedded in that portion of the prox- 

 imal nectocalyx which forms the upper boundary 

 of the hydroecium, while from the smaller ciliated 

 chamber two ducts are given off, one to the distal, 

 the other to the proximal nectocalyx, where 

 each communicates with the small cavity common 







