EGGS OF FISHES 



185 



Bolau.* The egg case of Callorhynchus (Fig. 191) is 

 essentially shark-like ; it is of spindle-shaped outline, and 

 its broad, fringing margin gives it an almost seaweed-like 

 appearance. The ^gg is believed to be deposited in deep 

 water. 



The spawning of but one of the three existing Lung- 

 fishes has been recorded. Ceratodus, according to Semon, 

 has a spawning season extending over several months ; it 

 deposits its eggs in shallow water, scattering them broad- 

 cast. The female fish is attended by several males, and 

 the emission of eggs and milt appears to be simultaneous. 

 The ^^g (Fig. 192) lacks a horny capsule, but is amply 

 protected by a thick, jelly-like hull. It hatches during the 

 second week. 



Eggs of Ganoids are shown in Figs. 193, 194. They 

 are encased in a jelly-like envelope, especially viscid in the 

 case of sturgeon. When deposited, they speedily adhere 

 to whatever they touch, and often remain attached until 

 the time of hatching. The spawning grounds are in 

 shallow water ; the fish occur in numbers during a few 

 days of May and June, each female attended by several 

 males : ova and milt are emitted simultaneously, at short 

 intervals. The eggs develop rapidly, hatching in about a 

 week. 



The eggs of Teleosts present the utmost variety in 

 number, form, membranes, and mode of deposition. In 

 some forms (Embiotocids, Blenniids, Cyprinodonts) they 

 may even develop within the ovarian tissue, establishing 

 there a ** placental " circulation. They have been fertilized 

 within the fish, the anal fin spine of the male having in 

 some cases been metamorphosed into a copulatory organ. 

 The eggs of Siluroids (Fig. 195) are generally of large size, 



* V. Ref. p. 241. 



