﻿April, 1857.] 



ELLIOTT SOCIETY. 



107 



delicate tubes communicating- directly with the stomach, and radi- 

 ating towards the periphery of the disk, where they usually anas- 

 tomose with a concentric tube passing around the margin. In the 

 Aeginidse, this tube is not only absent, but the radiating tubes 

 themselves are represented only by short pointed projections of 

 the digestive cavity, while in many of the fixed Hydroidea, 

 there is neither any true digestive cavity, nor any circulatory 

 canal, both of these systems being represented by a simple blind 

 diverticulum of the larva's nutrient canal. 



The nervous system is hardly known. Professor Agassiz has 

 described as such a cellular cord which accompanies the circular 

 tube and enlarges at intervals at the bases of the tentacula to form 

 ganglion-like bodies which are also in connection with the ocelli 

 when present. I have also made out this cord in the genus 

 Eucheilota with distinctness, and I think also that I have done 

 so in Hippocrene and Nemopsis, but was not so successful 

 with Oceania, where however I have thought myself sometimes 

 able to trace a delicate cord passing down beneath the radiate 

 tubes. PL 12, fig. 1, 2, ^exhibits aportion of this system in Euchei- 

 lota where it will be seen that there is a ganglion for each margi- 

 nal sense-capsule. The sexual glands, whether ovaries or sper- 

 maries, are always situated between the walls of the digestive or 

 circulatory organs, and the epithelium of the inferior surface of 

 the body. They vary considerably in position, sometimes embrac- 

 ing the digestive cavity, sometimes the radiating tubes, sometimes 

 being in connection with both of these at once, and in one genus, 

 are connected with the radiate and marginal tubes at their junc- 

 tion. In Cunina and Aegina, &c, where the tubes do not exist, 

 these glands are situate on the periphery of the depressed digest- 

 ive cavity. In the most rudimentary fixed forms, they surround the 

 blind diverticulum of the larva's nutrient canal, which we have 

 already spoken of as representing both the digestive and circula- 

 tory systems. The spermatozoa of some species have been de- 

 scribed; they have very much the form of thread-cells with the 

 threads extended, but without the reverted hooks at the base of the 

 lash. The ova appear to be impregnated within the sexual gland 

 and are not discharged until they have reached the form of a round 

 or ovoid embryo. This is sometimes ciliated and capable of in- 

 dependent motion, (Planula,) sometimes it merely falls to the 



* See also the structure figured in this volume. PI. 7, ff. 34, and 42. 



