102 



COMPARATIVE ANATOMY 



CHAP. 



Testes and ovaries are, taken as a -whole, very simply constructed ; 

 ttey are vesicles or spheres, with numerous egg and sperm cells at 

 different stages of development. 



In Hydra both sorts of sexual products lie in the deeper part of 

 the body epithelium. In the other colonial Hydroids they are met 

 J. mth in specially shaped so- 



" /^^~\ ^ ^.^ called medusoid individuals, of 



which more will be said below, 

 either being formed primarily 

 in these individuals, or reaching 

 such a position secondarily from 

 the stem. 



In all Medusce the sexual 

 glands or gonades show, by 

 their position, a close relation 

 to the nutritive gastro- canal 

 system. In the Craspedota (Fig. 

 77), they lie in varying numbers 

 either on the wall of the oral 

 tube (Narcomedime and Antho- 

 medusce), or on the radial canals 

 {Leptomedusce and Trachomedusce). 

 Where there are 4 radial canals 

 there are 4 gonades, and where 

 there are 8 radial canals, 8 

 gonades. With increase in the 

 number of radial canals there 

 may also be increase in the 

 number of gonades. In the 

 Acraspeda 4 (less frequently 8) 

 globular or band -like gonades 

 are usually developed ; these 

 are sometimes folded, or curled, 

 or clustered, and occasionally 

 of considerable size ; they lie 

 in the subumbrellar wall of the 

 gastro-canal system, sometimes nearer the circumference, at other times 

 nearer the central gastric cavity. In the Felagidce and Cyanidm the 

 gonades hang down as 4 gastro-genital sacs from the subumbrella into 

 the umbrella cavity ; in the Bhkostomce and Aurelidce, on the contrary, 

 they lie on the upper surface of the subgenital cavities or the sub- 

 genital porticus (Fig. 70, p. 85). In the Craspiedota the ripe genital 

 products pass directly out into the umbrella cavity by the bursting of 

 the gonade ; in the Acraspeda they pass inward into the cavity of the 

 gastro-canal system, and reach the exterior thence through the mouth. 

 The sexual organs of Corals lie in the septa, near the free edges 

 which project into the gastral cavity. 



Fig. 77. — Eucope campanulata, partly after 

 Haeckel. A, From the surface. J5, Section in the 

 direction a-&-c of Fig. A. a-&,Perradius; &-c,adradius; 

 t, tentacle ; sh, marginal vesicle ; g, gonades ; mr, 

 gastric peduncle ; r, radial canals ; ;', velum ; ri, 

 circumferential canal ; tx, exunibrella ; sw, sub- 

 umbrella ; ga, jelly ; tg, tentacular vessel ; &-&, 

 principal axis. 



