EGGS. 79 



outer surface of their remains. Iu Bombinator, Hi/la, 

 and Rana the embryo develops much further within 

 the egg-, and becomes liberated by its own action. 



In Alytes, which is exceptional among European 

 Batrachians in the eggs being laid on land in strings, 

 taken charge of by the male parent, who carries them 

 about twisted round the legs, all the embryonic stages 

 are passed through within the egg, and the young is 

 born as a true tadpole. Contrary to the other Batra- 

 chians, the food-yolk of which is in insufficient quantity 

 to form an external appendage of the embryo, we find 

 here a large yolk-sac. These eggs, which measure 

 three and a half or four millimetres in diameter, are 

 of a uniform yellow colour, and are protected and 

 connected in rosary-like fashion by a comparatively 

 tough but highly elastic transparent investment, 

 which represents the adhesive envelop of the typical 

 Batrachian ovum, and contracts thread- or hair-like 

 between every two eggs. 



The following synopsis shows the principal dif- 

 ferences between the eggs of the European species, 

 and will serve to their identification, the dimensions 

 given being those of recently deposited ones. 



I. With large unpigmented vitelline sphere, 3^ — 4 

 millimetres in diameter, laid on land in rosary- 

 like strings, carried by the male twisted round 

 his legs, the larva leaving the envelops in an 

 advanced condition after the loss of the ex- 

 ternal gills and the formation of the spiraculum. 



Alytes. 



II. AVith small vitelline sphere (1 — 3 millimetres in 



diameter), entirely or partially brown or black, 



deposited in the water, the embryo leaving the 



envelops with external gills or before their 



appearance. 



a. Deposited singly or in small groups of two to 



twelve ; vitellus brown or black above, white 



or yellowish beneath, the embryo leaving the 



