GIG ANATOMY OF VERTEBRATES. 



year.' l Although the Emydians lay once every year, soon after the 

 period of copulation in the spring, the coitus is repeated a second 

 time every year in the autumn, shortly before the species return to 

 their winter quarters : and Agassiz concludes that in Emydians ' a 

 repetition of the act twice every year, for four successive years, is 

 necessary to determine the final developement of a new individual. 



118. Oviposition of Reptiles.- -\ do not know particulars of 

 this process in the Perennibranchiates. Some Newts (Triton 

 cristatus, e. g.) deposit the eggs upon aquatic plants (Polygonum. 

 Persicaria, e. g.), folding the leaf by means of the hind feet in 

 such a way that its under surface is turned inward, and the fold 

 made to stick by the adhesive coating of the egg which she inserts 

 in the fold. Our smaller Newt (Lissotriton punctatus, Bell) fre- 

 quently glues the egg in the axilla of the leaf. 2 



Oviposition of the Frog takes place during the sexual embrace 

 at the bottom of the water : as each egg is extruded, it is fertilised, 

 and, the chorion absorbing water, the egg acquires a diameter of 

 about three lines, the coloured vitellus appearing as a dot in the 

 middle of the transparent jelly : the ova adhere together in a 

 mass, and this is usually floated to the surface by disengagement 

 of gas in the substance of the glairy envelope. 



The ova are excluded under similar circumstances in the Toad; 

 but in a long string of jelly, in which they are arranged alter- 

 nately in a double series ; the string may be a sixth of an inch in 

 diameter and from three to four feet in length. In the obstetric 



o 



Toad (Alytcs), the male impregnates in water, assists in the exclu- 

 sion of the eggs, causes them to adhere to his own hind legs by 

 small pedicles, and then seeks the land : only when embryonic 

 developement is sufficiently advanced does he leave his place of 

 concealment, and betake himself to the water with the young brood 

 with which he has charged himself. The male Pipa is asserted to 

 place the eggs upon the back of the female, which give the stimulus 

 to the formation of the cutaneous cells in which the whole course 

 of metamorphosis is completed, fig. 367. In Opistliodelpliys and 

 Nototrema, the ova are transferred to the common pouch of the 

 dorsal integument, described at p. 588. 



The common Hinged Snake (Natrix torquata) excludes the eggs, 

 sixteen to twenty in number, connected together by a glutinous 

 coating, usually in some fermenting mass of decaying organic 

 matter, whereby they are often transported and spread abroad in 

 the manuring of fields and gardens. The Viper is not subject to 

 this ovipositing cause of dispersion, and the confinement to a limited 

 locality would seem to be the condition of the viviparity of most 



1 ccc. Part iii. p. 491. 2 cccxvu. 



