XI 



PRACTICAL HINTS— AMPHIBIA 



569 



Such internal fertilization leads up to the condition in the Salamanders 

 where fertilization takes place in the upper part of the oviduct and 

 the developing embryo is retained for a less or more prolonged period 

 within the body of the parent. In Salamandra maculosa larvae 

 about an inch in length are born in May resulting from fertilization 

 during the preceding summer. 



As in the Anura wide differences exist in the richness of yolk 

 and consequent size of the egg — the latter varying from under 2 mm. 

 in the Newts to 6 mm. (Necturus) or 7mm. in diameter (Cryptobranchus 

 japonicus) : so that here again though not to the same extent as in 



e.g. 



Fig. 254. —Tadpole of unknown Frog from Tropical Africa. 



A, side view ; B, ventral view, b.c, buccal cavity ; c.o, cement organ ; a, anus ; 

 E, eye ; e.g t external gill ; olf, olfactory organ ; op, operculum. 



the Anura there is* an excellent field for investiga- 

 tion into the influence of yolk upon developmental 

 processes. 



The eggs of Urodeles are commonly collected 

 under natural conditions and kept in earthenware 

 dishes. Or the adults just about to breed may be 

 brought into the laboratory and allowed to deposit 

 their eggs in a suitable aquarium. 



The Urodela form one of the relatively primi- 

 tive groups of Vertebrates and their embryology 

 deserves much greater attention than it has hitherto 

 received. Most of the older literature deals with 

 special details in the development of the Newts but comprehensive 

 monographs, including " normal plates " on the development of such 

 genera as Proteus, Siren and Amphiuma are much wanted. A 

 general account of the development of the American species of 

 Cryptolranchus has been given by Smith (1912), while the Japanese 

 species has been dealt with by Ishikawa (1918), De Bussy (1915) and 

 Dan. de Lange, Jr. (1916). Of Necturus normal plates with 

 accompanying tables have been worked out by Eycleshymer and 

 Wilson (1910). 



The Gymnophiona — though an aberrant group of Amphibians 

 highly specialized for a burrowing existence— are of much embryo-. 

 logical interest and have provided the material for work of great 

 morphological importance, such as that of Brauer upon the excretory 

 organs. A general account of the development of Ichthyophis 



