1 78 The Field Naturalist's Qtiarterly Aug. 



British Reptilia. (Reproduction.) 



I. Ophidia, Snakes. 



1. Vipera berus, the adder, is ovo-viviparous. 



2. Tropidonotus natrix, the ring snake, is oviparous. 



3. Corotiella atisiriaca, the smooth snake, is ovo-viviparous. 



II. Lacertilia, Lizards. 



1. Angiiis fragilis, the slow- worm, is ovo-viviparous. 



2. Lacerta vivipara, the common lizard, is ovo-viviparous. 



3. Lacerta agiiis, the sand lizard, is oviparous. 



It is thus seen that we have one snake (the ring snake) 

 which deposits eggs ; and one lizard (the rare sand lizard) 

 which likewise reproduces by the oviparous method. The 

 remaining four reptiles are all ovo-viviparous, bringing forth 

 their young alive. 



The mention of the two methods of reproduction naturally 

 suggests the idea that some reptiles are like birds in this 

 matter, whilst others — those which bring forth living young 

 — approximate more to the mammals in this particular 

 character. But the resemblance is more apparent than 

 real, especially in the case of the ovo-viviparous members, 

 in which the reproductive process differs essentially from 

 that in the higher mammals. In the reptile the growing 

 embryo is in the egg during the whole period of develop- 

 ment, deriving its nourishment from the yolk of the egg, 

 and rupturing the egg- membrane when fully developed. 

 This condition is actually found in the lov/est mammals, 

 the Monotremes of the Australasian region, which in their 

 reproduction approach the reptilian type ; but these peculiar 

 creatures are oviparous, laying or depositing eggs after the 

 manner of the ring snake. The process in the adder and 

 other reptiles which bring forth living young is not at all 

 comparable to the process in the higher mammals, and 

 indeed the main resemblance is that these reptiles retain 

 their eggs in the body during development instead of de- 

 positing them exteriorly. The nourishment is still derived 

 from the egg yolk, not by means of the special organ, 

 the placenta, which serves to nourish the mammalian 

 embryo. 



