82 INTRODUCTION. 



i • 



2. Envelop 7—10 millimetres in diameter 

 embryo brown or blackish . . . liana. 



(a) Vitellus miparti, brown or blackish 



above, yellowish or white below, or 

 the light spot covering at least the 

 lower third ; eggs submerged. 



Diameter of vitellus 1^ — 2 millimetres. 



B. esculenta, B. arvalis. 



Diameter of vitellus 2 — 3 millimetres . B. agilis. 



(b) Vitellus nearly entirely black, with a 



small whitish lower pole. 

 Diameter of vitellus 2 — 3 millimetres; eggs float- 

 ing B,. temporaria. 



Diameter of vitellus 1^ — If millimetres; eggs 



submerged B. latastii. 



It may be noticed that, so far as species are con- 

 cerned, the size of the egg stands in no relation to 

 that of the parent, a fact which is also conspicuous in 

 the tadpole. Tims the largest Batrachian, Bufo vul- 

 garis, has eggs no larger than the smallest, Belo- 

 dytes punctatus ; and in Bana temporaria, they are 

 considerably larger than in B. esculenta, which reaches 

 both in the larval and perfect states to a much greater 

 size. Heron-Royer has observed that young females 

 produce eggs of a somewhat smaller size than those 

 of full-grown specimens of the same species, and 1 

 have been able to verify his observation on Bana 

 temporaria. 



The number of eggs also varies according to the 

 size of the female. Heron-Royer, who has counted 

 them in most of the European species, gives the 

 following numbers as the result of his computation : 



Bufo viridis 10,000—12,000 



Bana esculenta .... 10,000 



Bufo vulgaris 4,972— 6,840 



Bufo ealamita 3,000— 4,000 



Bana temporaria .... 2,856 — 4,005 

 Pelobates fuscus .... 1,200— 2,236 

 Bana arvalis 1,000— 2,000 



