486 TELEOSTEI [CH. 



often swollen into a kind of urinary bladder which descends to open 

 behind the anus by a separate opening. The testis has a duct 

 which issues from its hinder end and unites with its fellow to open 

 by a genital opening between the anus and the kidney opening 

 (Fig. 238). 



The researches of Prof. Kerr on some of the more archaic types 

 of Osteichthyes have made it probable that the testis duct is to be 

 looked on as a posterior sterile extension of the testis itself, and 

 sections of the " duct " confirm this, because it is seen to be more 

 of the nature of a network of tubes than a single duct. According 

 to Jungersen it opens into the kidney duct in the embryo, and this 

 connection may be regarded as a single posterior vas efferens ; the 

 portion of the genital duct close to the opening may be regarded as 

 a split-off portion of the kidney duct. 



In the female the ovary is similarly continuous with a short 

 wide oviduct which joins its fellow to open by a genital opening. 

 But in some primitive families of Teleostei, such as Salmon and 

 Eels, the oviduct is absent and the ovary dehisces its ova into the 

 splanchnocoel, and, as in Cyclostomata, the ova escape by abdo- 

 minal pores. Investigation into development shows that the 

 oviduct arises as a groove in the peritoneum leading to the pore, 

 and that this groove is bounded on one side by a fold which is 

 nothing more than a sterile extension of the ovarian ridge itself. 



The brain of a Teleostean differs from that of Chondrichthyid 

 fish (1) in the reduction of the cerebral hemispheres to their basal 

 portions, which correspond to the so-called corpora striata in the 

 human brain. The roof of the cerebrum is a thin sheet of non- 

 nervous membrane continuous with the roof of the third ventricle ; 

 (2) in the solution of the optic chiasma. This, it may be remem- 

 bered, is a band of nervous tissue grooved off from the floor of the 

 thalamencephalon, in which run fibres from both eyes to both sides 

 of the brain. In the Teleostean this is split into two separate nervous 

 stalks each connecting one eye with the opposite side of the brain 

 only. Since the eyes of a Teleostean fish owing to its compressed 

 shape receive images of quite different objects, it is of no use trying 

 to combine them ; (3) in the protrusion of the cerebellum forwards 

 into the cavity of the mid-brain as the so-called valvula cerebri. 



In the cranial nerves the sole point which calls for remark is 

 a cutaneous branch of the 5th, which is distributed to -the bases 

 of all the paired and unpaired fins where there are developed 

 taste-buds. 



