OIVGANS OF GENERATION. 



421 



which unite, intimately along the upper aspect 

 of tlu> oruan, lull leave inli i lorly a deep fissure 

 \\lncli is continued to tlic extremity. In the 

 Cliflnniit tins on-an i if excitement is vcr. 

 and terminates in a lingle point, but in many 

 Xnii>-i<tit and O/I//I'<///IH specie- Us cxtiemity is 

 bitid, each division being covered with sharp 

 and ice nned spines, an arrangement which, in 

 creatures so deficient in organs of prehension, 

 is c\ idctitly adapted to ensure efficient copu- 

 lation. 



In the females of these reptiles the structure 

 of the oraria is interesting, gradually leading us 

 from the folds of vascular membrane, between 

 winch the numerous eggs of the Batrachia are 

 p in rated, to the form which they present in 

 llirds. Each ovary assumes a racemose ap- 

 pearance, and consists of a number of ova in 

 various states of perfection, which are loosely 

 attached to the sides of the vertebral column by 

 folds of peritoneum. Their structure, however, 

 is essentially that which lias beeu already de- 

 scribed, and the ova, when matured between 

 the vascular laminx of the ovarian investments, 

 escape, as in frogs, from the surface of these 

 viscera by a laceration of the investing mem- 

 brane, and would break loose into the abdo- 

 minal cavity did not the more perfect develope- 

 mcni of the oviducts, which here have their 

 patnlous extremities so disposed that they can 

 gra-sp the ovaria during excitement, prevent such 

 an occurrence, by receiving the perms imme- 

 diately from the ruptured ovary. The oviducts 

 are two in number, membranous at first, but 

 glandular as they approach their termination 

 in the cloaca. In these the eggs receive an 

 albuminous investment which they absorb in 

 the first portion of the canal, and prior to their 

 expulsion are furnished with a coriaceous or cal- 

 enioiis covering produced from the thicker 

 portion of the oviferous tube. 



The females of the Chcltmia have a clitoris, 

 or rudiment of the male penis, which is in a 

 similar manner provided with muscles for its 

 retraction into the cloaca after extrusion. In 

 other Reptiles the clitoris is deficient. 



Birds form a remarkable exception to the 

 usual arrangement of the internal sexual organs 

 in oviparous vertebrata, the ovarium and oviduct 

 bcin<.; single throughout the class, an organi- 

 zation which is evidently in relation with that 

 lightness and activity essential to their habits. 

 This deviation from the usual type, however, 

 is only apparent, arising from the non-develop- 

 ment of the ovary and its duct on one side of 

 the body, although both exist in a rudimentary 

 state. 



The ovarium, as in Reptiles, is racemose, 

 con-isting of ova in different stages of growth, 

 each enclosed in a vascular membrane, which 

 forms a pedicle attaching it to the general 

 cluster, and is ruptured by the escape of the 

 germ enclosed within it. The oviduct is short in 

 comparison with that of many reptiles, and the 

 structure of its lining membrane indicates the 

 otliees performed by different portions of the 

 canal, being smooth and vascular in its upper 

 portion, where the yolk receives its albuminous 

 COM niis, but becoming villous and plicated 

 where it secretes the shell. 



Male birds, like reptiles, are furnished with 

 tef, which, from their comparatively in- 

 significant size, do not materially interfere with 

 the bulk of the viscera; yet even these only a- 

 sume their full proportions at stand time-, 

 namely, at that period of the year when their 

 office is required. 



The testes are constantly situated in the ab- 

 dominal cavity immediately behind the lungs 

 and under the anterior extremity of the kidney : 

 as in all cases, they consist of sperm-secreting 

 tubes, but of such extreme tenuity that their 

 diameter was estimated by Miiller as not 

 greater than the 0'00528 of a Parisian inch. 

 These canals are enclosed in a proper capsule, 

 which sends septa into the interior of the organ ; 

 they unite to form a slightly Hexuous vas defe- 

 rens, which accompanies the ureter of the cor- 

 responding side. The vasa deferentia termi- 

 nate by separate orifices in the cloacal cavity 

 near the root of the rudimentary penis when 

 such exists, but even in its roost perfect forms 

 the male organ is merely an instrument serv- 

 ing for the conveyance of the seminal liquor 

 along a groove seen upon its surface, there 

 being as yet no corpus spongiosum or inclosed 

 urethra as in the Mammiferous classes, adapted 

 to an efficient injection of the semen into the 

 female parts, nor any auxiliary secretions sub- 

 servient to the same puq>ose. In the females 

 of those genera in wliich the penis is most de- 

 veloped, a clitoris is found to occupy a similar 

 position. 



The Mammalia differ remarkably from the 

 other vertebrate classes in the elaborate deve- 

 lopement of the sexual organs in both sexes. 

 The increased complication of these parts is attri- 

 butable in the male to the necessity for a much 

 more efficient intromission of the spermatic 

 secretions during coitus, and in the female to 

 the superaddcd function of gestation which 

 characterizes the class. 



On comparing the male organs of Mammi- 

 fera with those of the oviparous vertebrata, 

 several circumstances demand our notice, the 

 most striking of which is the separation of the 

 canals provided for excretion into two distinct 

 systems, each terminating externally by an 

 appropriate orifice, thus detaching entirely the 

 digestive emunctory from the genito-urinary 

 apparatus, which hitherto we have found to dis- 

 charge themselves by one common orifice com- 

 municating with a cloacal cavity. With one 

 interesting exception furnished by the Mono- 

 trernata, such a separation exists throughout all 

 the Mammiferous orders. Internally a still 

 further isolation is evident in the separation of 

 the urinary and generative organs by the pro- 

 vision of a urinary bladder, in which the secre- 

 tion of the kidneys is stored up until its expul- 

 sion becomes necessary ; the same excretory 

 canal, however, is still common to both these 

 systems. In the ovipara the penis was merely 

 furrowed with a sulcus, along which the semen 

 trickled during the union of the sexes without 

 being impelled by any expulsive apparatus ; 

 but in the class of which we are now speaking 

 the urethral canal becomes surrounded by vas- 

 cular erectile tissue, forming a complete tube 

 through which the seminal liquor is powerfully 



