DEVELOPMENT OF JELLY-FISHES. 63 



nervous system is present in the MquoridcB and Mginidce, 

 but is most distinct and best developed in the Oeryonida 

 {Glossonodon and Carmarina). 



The Hertwigs have also observed in these Trachynemidse 

 organs of taste, consisting of groups of long stiff hairs at 

 the base of the tentacles. They have been observed in 

 RJiopalonema velatum, Aglaura nemistoma, and in Ounina, 

 where the hairs are shorter. 



The eggs, in developing, after total segmentation (morula 

 state) pass into a ciliated planula state as in Aurelia, there 

 being at first apparently no primitive gastric cavity ; the 

 body of the embryo or planula remains spherical, as in Oery- 

 onia, there being a slight metamorphosis ; or, as in Poly- 

 xenia and ^ginopsis, where there is a decided metamor- 

 phosis, the spherical ciliated planula greatly lengthens out 

 on each side, the body becoming boomerang-shaped, each 

 end of the boomerang becoming an arm or tentacle. Then 

 it becomes a gastrula, a central cavity and mouth appear- 

 ing. At right angles to the two primitive arms bud out 

 two others, and finally others appear on the lower edge of 

 the umbrella, and after slight changes the adult form is as- 

 sumed. Cunina is at first spherical, then, a single arm 

 developing, it becomes club-shaped ; finally, the full num- 

 ber of arms grow out, and the mature form results. It ap- 

 pears, then, that in the mode of development from eggs, 

 without passing through a hydra-like condition, and in the 

 structure of the body, the Tr achy medusa connect the cov- 

 ered-eyed medusae with the naked-eyed or Hydroidea. The 

 American forms are found from Newport southward. A 

 probably exotic fresh-water form (Limnocodium) lives in a 

 tank (90° P.) at London. Cunina has been found by 

 Haeckel growing on the columella of Geryonia, and 

 McCrady has found that our native Cunina is parasitic on 

 Turritopsis, a hydroid medusa. 



The LucernaricB, or Calycozoa, which, according to Clark, 

 form an order of Acalephs, are, with Huxley, regarded as 

 a suborder of Discophora. With essentially the structure 

 of the Aurelia and allies. Lucernaria differs in having the 

 power of attaching itself by a sucker on the smaller end of 

 its body to sea-weeds, but can detach itself at will and swim 



