of Echinorhynchus gigas. 443 



dorsal and a ventral) attached to the body, and are in con- 

 tact and united in the middle. Anteriorly the two sacs 

 communicate, and their membranes separate entirely from 

 the walls ; they form a point like a nightcap, which finally 

 advances to the proboscis. Posteriorly the conditions are 

 more complicated, but an arrangement is made by which both 

 sacs communicate with the uterine bell. These sacs alone 

 contain the ova and free-swimming ovaria. The two lateral 

 three-cornered spaces are to be regarded as the body-cavity. 

 Where the two sacs are attached in the middle of the body, 

 there is a finely granular cord, which, in the young state, 

 contains a series of very fine large nuclei. This cellular cord 

 is called the ligamentum in many Echinorhynchi^ and has 

 been interpreted as the ovary by several observers. I shall 

 hereafter endeavour to show that it rather represents the 

 intestine. In EcJiinorhynchus gigas the nuclei of the cord 

 ultimately become completely obliterated, whilst in other 

 species they persist. The males possess a similar arrange- 

 ment ; but I shall not enter upon that. The analogy between 

 the mxale and female sexual organs is nearly complete ; but 

 as the comparative size of the individual parts is very difter- 

 ent, it becomes difficult to establish this, or to make it clear 

 without a considerable number of figm'cs. 



The hooks grow outwards from the innermost layer of the 

 proboscis. When they are already formed and calcified, they 

 are still covered by a thin membranous layer, which they 

 afterwards cut through so as to become perfectly free. It is 

 only then that the proboscis becomes inverted. 



Any one who goes thoroughly into the anatomy of the 

 EcJtinorhgnchi will find how difficult it is to compare the 

 structure of their body with that of any other animal. This 

 is not due to deficient knowledge of their structm-e, but pro- 

 bably rather to the fact that we require to know a series of 

 other animals which constitutes their connexion with allied 

 forms. Perhaps, indeed, the EcMnorliyncM are not simple, 

 but double animals — in this fashion, that the proboscidal ap- 

 paratus represents one, and the so-called sexual organ the other 

 animal, whilst the body-envelope is common to both. Both 

 animals are mouthless, and each of them is modified for a 

 special purjDOse. Similar conditions, as is well known, occur 

 among the Bryozoa. The developmental history is exceed- 

 ingly favourable to this supposition ; but its more exact de- 

 monstration I must leave for a detailed memoir. 



32^ 



