570 EMBEYOLOGY OF THE LOWEE VEETEBEATES ch. 



will be found in Sarasin (1887-90) and of Hypogeophis in Brauer 

 (1897). 



The eggs, fertilized internally, are normally deposited in the soil 

 and the embryologist has, as a rule, to depend upon such scanty 

 material as can be obtained by digging in the damp soil of localities 

 where Gyumophiona are abundant. Typhlonectes in South America 

 and Dermophis in West Africa are viviparous. 



Of the group in general it may be said that a comprehensive 

 monograph on the development of each genus beyond Ichthyophis 

 and Hypogeophis is a great desideratum. 



As standard fixing agents for Amphibia corrosive sublimate and 

 acetic acid, and for the later larval stages strong Flemming's 

 solution, may be used. For the early stages (segmentation and 

 gastrulation) quite good results are obtainable from eggs that have 

 been preserved alive in 10*/ formalin : in this case it is well to treat 

 the egg before dehydration for an hour or two with corrosive 

 sublimate solution as without this precaution the formalin-preserved 

 eggs are difficult to stain well. When any other fixing agent than 

 formalin is used it is necessary, as a preliminary, to remove the egg 

 envelopes. In the case of the larger eggs of the Urodela and 

 Gymnophiona this can be accomplished with the aid of fine scissors 

 and forceps. 



Eeptilia. — For gaining practical knowledge of Eeptilian 

 development the student will find the group Chelonia most con- 

 venient as it is possible to obtain 1 excellently preserved series of 

 developmental stages of Terrapins (Chrysemys) and Snapping Turtles 

 (OJielydra). In particular localities especially in warm climates he 

 may have opportunities of obtaining the eggs of Lizards, Snakes or 

 Crocodilians. In all cases the same technique may be used as in the 

 case of the Fowl. 



Aves. — The Birds, although showing conspicuous differences in 

 external appearance and in minute details of structure, form a very 

 compact evolutionary group and there is little likelihood of important 

 differences in principle existing iri their development. Interesting 

 differences in detail however are to be found — such as the presence 

 or absence of neure,nteric canals. Groups which there is any reason 

 to suspect of being particularly archaic — such as Divers, Grebes, 

 Penguins — are worthy of careful scrutiny for possible persistence of 

 Eeptilian features. 



LITERATURE 



Bles. Trans. Roy. Soc. Edin., xli, 1905. 

 Brauer. Zool. Jahrbueher (Anat.), x, 1897. 



de Bussy (de Lange), L. P. Eerste ontwikkelingsstadien van Megalolatrachus 

 Maxiinus, Schlegel. Amsterdam, 1905. 



Cerfontaine. Arch, de Biologie, xxii, 1906. 

 Dean, Bashford. Journ. Morph., xi, 1895. 



1 E.g. from Mr. J. C. Stephenson/Washington University, St. Louis, or The-Marine 

 Biological Laboratory, "Wood's Hole. 



