712 EEPTILIA. 



(2014.) The finny tribes, incapable of social intercourse, were content 

 with the simple extrusion of their eggs into the sea, leaving them to be 

 impregnated by the casual approach of a male of the same species ; but 

 even in the Amphibious reptiles some steps are gained in associating 

 the sexes with each other ; and although the eggs are still impregnated 

 out of the body of the mother, in the Frog this is accomplished in eccitu, 

 and not subsequent to their expulsion. 



(2015.) Frogs, during the breeding-season, are found to pair, and 

 the male having selected his mate mounts upon her back, clinging to 

 her with unwearying pertinacity during the whole period of oviposition, 

 and vivifying her eggs by the aspersion of the seminal secretion as they 

 are successively expelled in long gelatinous chains. During this pro- 

 tracted embrace the male Frog is assisted in retaining his hold by the 

 development of a peculiar papillose structure upon the first toes of the 

 fore-feet, which disappears at the end of the time appropriated to repro- 

 duction. Of course no intromittent apparatus is as yet required, and we 

 may naturally expect to find the male organs still exhibiting great 

 simplicity of construction. 



(2016.) The testes and their excretory ducts, in fact, are the only 

 parts as yet met with ; but the anatomy of these parts, although most 

 accurately investigated by Swammerdam upwards of a century ago, is 

 still very generally misunderstood. The testicles are situated in the 

 loins, surrounded by several tongue-like masses of fat presenting a 

 peculiar granulated appearance. Each testis is invested by a delicate 

 capsule, and on removing this very carefully, the entire viscus is seen 

 to be made up of short caeca, the blind extremities of which alone 

 appearing at the periphery of the organ caused Cuvier to describe it as 

 being "an agglomeration of little whitish grains interwoven with blood- 

 vessels." The semen elaborated by these cseea is taken up by several 

 small excretory ducts that pierce the kidney, in the immediate vicinity 

 of which the testis lies, and open into the ureter, that here forms the 

 common excretory duct, whereby the urine as well as the seminal fluid 

 is discharged, both escaping into the cloaca at a little distance from the 

 orifice of the allantoid bladder, to be ultimately ejected through the vent. 



(2017.) Neither is the generative system of the female Frog less 

 worthy of notice. The ovaria resemble in their essential structure those 

 of the Lamprey ( 1846); only they are much less extensive, consisting 

 of a few festoons of the highly vascular membrane wherein the ova are 

 secreted, fixed at the pelvic extremity of the abdominal cavity. On 

 each side of the body is a long and very tortuous oviduct, which when 

 unravelled is found to be many times the length of the animal. The 

 fimbriated commencement of this oviduct is firmly bound down by folds 

 of peritoneum in the immediate vicinity of the pericardium, and, of 

 course, as remote as possible from the ovary ; it therefore becomes a 

 question of no inconsiderable interest to determine the manner in which 



