COPCLATORY ORGANS. 327 



a continuation of the fibres of the internal oblique and transver- 

 salis. When the inguinal canals become obliterated, the testes 

 remain throughout lite in the scrotum. 



In many Mammals, however, the testes remain permanently 

 within the abdomen. Their size is not always proportionate to 

 that of the body ; they are smooth, and somewhat oval in form, 

 and are covered by a fibrous investment (Fig. 255, A}, from which 

 processes (trabeculae) usually extend inwards. In this way the 

 seminal tubes are separated into definite bundles (Z, Z), and a sort 

 of lattice-work is also formed (corpus Highmori, f), by means of 

 which the elements of the rete Halleri (that is, the vasa 

 efferentia, Ve) pass to the epididymis (-VZf). 



In the epididymis the seminal tubules become rounded off to 

 form the so-called coni vasculosi, and these are connected to- 

 gether by a collecting duct, the vas epididymis (Fig. 255, Cv, 

 Cv, Vep). The vas deferens ( Vd) arises from the last conus vas- 

 culosus, and gives rise towards its distal end, shortly before it. 

 opens into the urinogenital sinus, to glandular outgrowths (vesi- 

 culae seminales), which may attain a relatively enormous size 

 in Rodents and Insectivores (Fig. 256, Sb). From this point to 

 its termination the seminal canal is spoken of as the duct us 

 ejaculatorius. 



In many Mammals rudiments of the Mullerian ducts are pre- 

 sent, and open into the urinogenital sinus. In some (e.g. Man), only 

 the most posterior end of the latter remain, in the form of an un- 

 paired vesicle (uterusmasculinus), which lies embedded within 

 an accessory genital gland, the prostate. This gland, which more 

 or less completely surrounds the urinogenital sinus, consists of 

 glandular tubules, connected together by means of fibrous and 

 muscular tissue : its secretion is poured into the urinogenital sinus 

 (compare Figs. 236, A to C, and 256). 



COPULATORY ORGANS. 



External organs of generation, such as are present in the higher 

 Vertebrates, are never found in Fishes, though in male Elasmo- 

 branchs a specially modified portion of the pelvic fin serves as 

 a copulatory organ ("clasper" or "pterygopodium"). It 

 consists of a series of cartilages which are moveable upon one 

 another, is covered by skin and muscles, and is provided with a 

 channel along the inner side. It must be looked upon as a deriva- 

 tive of the fin-rays. * 



These claspers are inserted, in a closed condition, into the 

 cloaca of the female, and thence into the oviducts; they are 

 then opened out by means of special muscles, and the seminal 

 fluid flows along their channels into the distended oviducts. In 



