102 



COMPARATIVE ANATOMY 



CHAP. 



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

 they 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 



with 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 Medusae 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 (Narcomedusce and Antho-\ 

 medusce), or on the radial canals j 

 (LeptomeduscesLiidTrachomedusce). 

 Where there are 4 radial canals 

 there are 4 gonades, and where j 

 there are 8 radial canals, 8 i 

 gonades. With increase in the j 

 number of radial canals there 

 may also be increase in the i 

 number of gonades. In the j 

 Acraspeda 4 (less frequently 8) 

 globular or band -like gonades j 

 are usually developed ; these 

 are sometimes folded, or curled, -i 

 or clustered, and occasionally ! 

 of considerable size ; they lie 

 in the subumbrellar wall of the j 

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

 nearer the central gastric cavity. In the Pelagidce and Cyanide?, the 

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

 the umbrella cavity ; in the Rhizostomw 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 Craspedota the ripe genital I 

 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, j 



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. B, Section in the 

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

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

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

 circumferential canal; ex, exumbrella; su, sub- 

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

 principal axis. 



