INDUCED BREEDING 99 



The eggs are deposited m a manner quite different from the frog in that they are layed 

 singly in long strings of jelly, each egg being inseminated by the male (during amplexus) 

 as it emerges from the cloaca of the female. It is therefore necessary to induce am- 

 plexus in toads and allow the paired animals to lay their eggs naturally. Amplexus may 

 be induced by injecting the male with doses of pituitary glands equivalent to those used 

 for the female, and placing the pair together in a small amount of water. Several changes 

 of the water may be necessary before the eggs are layed, to eliminate the faecal and 

 other matter in the water. The water should be appropriate to survival of sperm and eggs. 



Hyla : 



The tree toads and other closely related species are difficult to secure out of breeding 

 season but if caught during or just before hibernation they may also be induced to lay 

 their eggs in the laboratory. The method is similar to that for Bufo and during amplexus 

 the male may be seen to bring his cloaca down close to the cloaca of the female as each 



gg emerges, indicating separate insemination of each egg. The Hyla egg is small but 



xcellent for operative procedures. 



e 

 ex 



Xenopus: 



This is the African clawed-toad which has attained fame through its use in pregnancy 

 tests. It is extremely sensitive to the pituitary hormone, and ovulation can be induced by 

 the pituitary (or gonad stimulating hormones) from any source. The method of inducing 

 the breeding reactions and caring for the early embryos has recently been described in 

 detail by Aronson (1944) Weisman and Coates (1944) and by Cameron (1947) whose papers 

 should be consulted. It is likely that the Xenopus egg and embryo will become increas- 

 ingly valuable as a laboratory form for experimentation purposes. 



B. URODELA 



Among the salamanders the eggs are generally inseminated as they pass through the 

 genital tract of the female, after she has picked up the sperm bundles (spermatophores) 

 dropped in the water by the males. Artificial insemination of the Urodele egg is possible 

 but rather difficult, since the sperm found in the spermatophores are not properly acti- 

 vated. The process of artificial insemination consists of the removal of activated sperm 

 from the genital tract of the female and applying them to oviduccal eggs of a pituitary- 

 stimulated female, not impregnated. The sacrifice of the several animals is necessary 

 and only a few eggs are secured. The more satisfactory procedure, therefore, is to 

 inject the pituitary hormone into females known to carry spermatophores, whereupon 

 they will deposit fertilized eggs. 



There are two methods which may prove of practical value in the production of fertile 

 eggs of the Urodela: First , pituitary stimulation of the male two days prior to the stimu- 

 lation of the female thereby causing it to deposit the spermatophores. If this is accom- 

 plished in a proper environment the females may be induced to pick up the spermatophores 

 with their cloacal lips after which they may be stimulated to ovulate. Second , some suc- 

 cess has been reported from Europe (Triton) where the paired animals are well fed, then 

 placed in the dark at hibernation temperatures (4° - 8°C. ) for a month or more, and then 

 are brought out into the light at Spring teinperatures (18° - 25°C. ), whereupon they will 

 spontaneously produce fertile eggs. 



Triturus : (pyrrhogaster, torosus* or viridescens**) 



These newts can be kept in the laboratory for long periods, are fed on liver and earth- 

 worms, and can be induced to ovulate either with amphibian (R. pipiens) pituitaries or 



* Now known as Taricha Torosa. 

 ** Now known as Diemyctylus viridescens. 



