166 



FISHES. 



In Chondropterygians (and Holocephali) the organs of re- 

 production assume a more compact form, and are more free 

 from a lengthened attachment to the back of the abdominal 

 cavity. The ovaries of the majority are paired, single in 

 the Carchariidce and Scylliidoe, one remaining undeveloped. 

 But the oviducts are always paired, beginning immediately 

 behind the diaphragma vrith a common aperture. They 

 consist of two divisions, separated by a circular valve ; the 

 upper is narrow, and provided within its coats with a gland 

 which secretes the leathery envelope in which most of 

 the Chondropterygian ova are enclosed; the lower forms 

 the uterine dilatation, in which the embryoes of the vivi- 

 parous species are developed. Generally the vitelline sac 

 of the embryoes is free, and without connection with the 

 uterus, which in these cases has merely the function of 

 a protecting pouch ; but in Carcharias and Mustelus Isevis a 

 placenta uterina is formed, the vascular walls of the vitelline 

 sac forming plaits fitting into those of the membrane of the 



Fig. 78. — Ventral tins and olaspers of Chiloscyllium trispeculare. 



uterus. The ends of the uteri open by a common aperture 

 behind the ureter into the cloaca. 



