MODIFICATIONS OF THE EEPEODUCTIVE OEGANS. Ill 



pi3nes are morphologically related to tliose of the higher 

 Vertehrata. 



In the female sex, the homologue of a penis frequently 

 makes its appearance as a clitoris, but rarely passes beyond 

 the stage of a grooved process with corpora cavernosa and 

 corpus spongiosiim — the former attached to the ischium, and 

 the latter developing a glans. But, in some few mammals 

 (e. g. the LemuridceJ, the clitoris is traversed by an urethral 

 canal. 



In no vei-tebrated animal do the ovaries normally leave the 

 abdominal cavity, though they commonly forsake their 

 primitive position, and may descend into the pelvis. But, in 

 many mammals, the testes pass out of the abdomen through 

 the inguinal canal, between the inner and outer tendons of 

 the external obliqiie muscle, and, covered by a fold of peri- 

 toneum, descend temporai-ily or peiinanently into a pouch 

 of the integument — the scrotum. In their course they be- 

 <j(ime invested with looped muscular fibres, which constitute 

 the cremaster. The cremaster retracts the testis into the 

 aljdominal cavity, or towards it, when, as in the higher 

 mammals, the inguinal canal becomes very much narrowed 

 (ir altogether obliterated. In most mammals the scrotal 

 sacs lie at the sides of, or behind, the root of the penis, 

 liut in the Didelj^hia the scrotum is suspended by a narrow 

 neck in front of the root of the penis. 



In most mammals the penis is inclosed in a sheath of 

 integument, the preindium ; and in many, the septum of the 

 corpora cavernosa is ossified, and gives rise to an as penis. 



In the female the so-called labia major a represent the 

 scrotal, the labia minora the preputial, part of the male 

 organ of copulation. 



Organs not directly connected with reproduction, but in 

 various modes accessory to it, are met vrith in many Verte- 

 hrata. Among these may be reckoned the integumentary 

 pouches, in which the young are sheltered during their 

 development in the male Pipefish [Syngnathus), in some 

 female Amphibia (Notodelplnjs, Pipa), and MarsMpialia ; to- 

 gether with the mammary glands of the Mammalia. 



