322 



REPTILIA. 



traordinary and apparently unnecessary length 

 of its canal. In the upper part of its course, 

 the walls of the oviduct secrete the albumen, 

 in which the yoke becomes enveloped, and 

 subsequently the membrana putaminis and 

 the egg-shell are supplied by its inferior por- 

 tions. In correspondence with these changes 

 of function, its lining membrane is found to dif- 

 fer in appearance and structure in different re- 

 gions of the oviduct. Towards the commence- 

 ment of that canal (fig. 65, p), it is exceedingly 



Oviduct of Emys Europceus. (After Bojanus.} 



A", commencement of oviduct; nop, canal of 

 oviduct laid open ; s t, ovum contained in lower 

 part of oviduct, broken to show the yolk, the albu- 

 men, and the egg-shell ; B, allantoid bladder ; c D, 

 kidney; E, ureter; F, oviduct; u, termination of 

 oviduct ; m, termination of the opposite oviduct laid 

 open. 



delicate, gathered into longitudinal folds, and 

 covered with vibratile cilia lower down (o) ; 

 the walls of the oviduct become evidently 

 glandular, and towards its termination (), 

 where the outer investments of the egg are 

 secreted, it is thrown into broad irregular rugae, 

 which are continued as far as its termination 

 in the cloaca (m). External to the mucous 

 membrane, there is a stratum of muscular 

 fibres, by the contractions of which the ovum 

 is propelled along the oviduct ; and externally 

 it is invested with a peritoneal tunic that ex- 

 tends throughout its whole length. 



The oviducts in the reptilia are very exten- 

 sible, and in many genera are constructed to 

 contain numerous ova at the same time, as 

 for example in lizards (Jig. 240, e). In ser- 

 pents, owing to the slenderness of their bodies, 



the numerous ova thus contained in the ovi- 

 duct are arranged in a very remarkable manner : 

 those lodged in the right oviduct correspond 

 with an unoccupied space in the left, and vice 

 versa those in the left are lodged in an inter- 

 space between the ova contained in the right. 



The reptilia proper differ in a very impor- 

 tant particular from the Amphibia in the 

 manner in which their eggs are fecundated: in 

 the latter, the fertilisation of the ova is ef- 

 fected after their exclusion, so that the en- 

 velope of the egg consists merely of a thin 

 chorion: but in the former, where impregnation 

 takes place internally, the ova, after being fe- 

 cundated, are provided with an external cover- 

 ing, the nature of which varies in different 

 races. Among the Chelonian reptiles, the 

 land and fresh-water tortoises produce eggs 

 covered with a hard calcareous shell like that 

 of birds ; but in the turtles, the outer shell 

 remains soft, presenting a texture something 

 like that of parchment. 



In crocodiles the egg-shells are calcareous 

 and brittle, but in the generality of Saurians 

 they are flexible and pergamentaceous. In the 

 Ophidians the egg-shells are made up of su- 

 perposed layers of soft membrane, secreted 

 by the walls of the oviduct. 



Some reptiles are generally but improperly 

 styled viviparous. The common viper, for 

 example, derives its name from the circum- 

 stance of its sometimes producing its young 

 alive. In this, and in all similar instances, 

 however, such an occurrence is merely for- 

 tuitous, and depends upon the length of time 

 the eggs are retained in the oviduct prior to 

 their expulsion. If they are not expelled 

 before the young are hatched, of course the 

 creatures bring forth their progeny alive ; and 

 the same animal may, from the nature of its 

 food, be made to produce eggs at one time and 

 living animals at another. 



The females of those reptilia whose males 

 are provided with a single penis are furnished 

 with a clitoris, but in those genera which 

 have the penis double or invaginated, this 

 organ is deficient. In the female Chelonians 

 the clitoris has very much the same struc- 

 ture as the penis of the male, from which 

 indeed it only differs in its smaller propor- 

 tional size : it is long, grooved throughout its 

 whole length along its dorsum, and terminated 

 by rounded glans on each side: it contains 

 peritoneal canals similar to those of the male, 

 and is moreover provided with muscles re- 

 sembling those of the male penis, by which it 

 is retracted into the cloaca. 



Thefemale crocodiles have likewise a clitoris 

 very similar to the male penis, but of much 

 smaller proportional dimensions. 



Development of the Embryo. As relates to 

 the internal structure of the egg, and de- 

 velopment of the embryo, the Reptilia differ 

 in no essential circumstance from the warm- 

 blooded Ovipara. Within the calcareous 

 or pergamentaceous egg-shell there is a con- 

 siderable quantity of exceedingly transparent 

 albumen, which so completely fills the shell 

 that no air bubble is to be 'detected in its 



