THE BREEDING HABITS OF ANIMALS 



193 



while in other salamanders the sperniatophores are deposited during am- 

 plexus. In a very large number of animals there is still further insurance 

 of fertilization, for the spermatozoa are transferred directly from the 

 male to the female (true copulation), fertilization taking place within the 

 body of the female. This method is employed by some parasitic worms, 

 snails, fishes, and amphibia, and by all of the insects, reptiles, birds and 

 mammals. 



Summary of Methods of Fertilization. — Notwithstanding the con- 

 fusion which this array of special devices and practices may seem to ex- 

 hibit, four well-defined general types of combination of place and mode 

 of fertilization may be recognized as follows: 



1. External fertilization without amplexus. — The eggs and 

 sperms are deposited freely in the water to come together by chance. 



Fig. 147. — Amplexus in a species of toad, Bufo typhonius (Linnaeus). The small in- 

 dividual is the male, the larger the female. Fertilization is external, the eggs and sperms 

 being emitted at the same time. Various other methods of clasping are represented among 

 forms with external fertilization, but this is the common one among the Salientia. {Photo 

 by A. G. Ruthven.) 



2. External fertilization with amplexus. — Amplexus may occur 

 some time before egg-laying, or the eggs may be laid during amplexus. 

 In the former case, the eggs are fertilized by spermatozoa stored in the 

 seminal receptacle of the female. In the latter case, they are fertilized 

 directly by the male. In either case fertilization takes place while the 

 eggs are being laid. 



3. Internal fertilization without copulation or amplexus. 

 The female takes into her body groups of spermatozoa previously de- 

 posited by the male. 



4. Internal fertilization w^ith copulation or amplexus. — The 

 spermatozoa a,VQ directly transferred from the male to the female (copu- 



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