Vol. 3] Torrey. — Biological Studies on Corymorplia. 



255 



hydroid. In common with the medusae of all hydroids where a 

 similar condition obtains, it shows signs of degeneracy. Tenta- 

 cles, sense organs and mouth are lacking, and the bell, in propor- 

 tion to the manubrium, is very much smaller than usual. Other- 

 wise the medusa is perfect. The bell not only possesses a ring 

 and four radial canals, but from an early stage of development 

 pulsates as vigorously as though it were free. Subumbrella 



Fig. 1. 



1 2 



Female medusa, with a number of uuripe eggs outlined on the 

 manubrium. X 58. 



Fig. 2. Male medusa at maturity. X 58. 



muscles still remain, therefore, and function actively — an inter- 

 esting persistence of a habit which the species appears to have 

 outgrown. 



As in C. pendula (May, :03), the germ cells arise in the 

 ectoderm of the manubrium from cells which are derived from 

 the ingrowing ectodermic plug at the apex of the medusa-bud. 

 Definitive ova result from the growth of some of these cells at 



