68 



SYSTEMATIC ZOOLOGY 



FlG. 51. Turritopsis nutricula, a craspedote me- 

 dusa, highly magnified. (Drawn from life by the 



author.) 



hydroids ; buds of this kind are called gonophores (Fig. 47, 

 1 b, 2, and 5). Furthermore, in some medusae the fertilized ova 



do not produce hydroids, 

 but develop directly into 

 medusae, and in some 

 cases new medusae are 

 even formed as buds 

 on the manubrium of 

 the parent (Fig. 47. _ 

 The hydroids often 

 have a cuticular shell 

 or skeleton with open- 

 ings through which the 

 polyps may be pro- 

 truded, and in a few 

 genera there is a skele- 

 ton of calcium carbon- 

 ate, thus forming a kind 

 of coral (Fig. 50). 

 Hydroids occur widely distributed on rocky shores, and are 

 also found in water of one hundred meters or more. Some live 

 on the shells inhabited by 

 hermit-crabs, and in this 

 way are carried about, 

 while their presence con- 

 ceals and thus protects 

 the crab (Fig. 47, 1 a). A 

 similar phenomenon has 

 been referred to under 

 the sponges. The me- 

 dusae of this order are 

 pelagic, i.e. they swim 

 near the surface of the 

 ocean. They are for the 

 most part small, only a 

 few millimeters in diame- 

 ter, though a few attain 

 < Figs. 48, 51, and 52). 



FlG. 52. Liriope, a craspedote medusa, highly 

 magnified. (Drawn from life by the author.) 



a diameter of several centimeters 



