TRITON 99 



anterior tubules of the kidney and so into the Wolffian ducts 

 which become the vasa deferentia. The more posterior 

 tubules of the kidney are solely excretory in function, and they 

 do not connect with the Wolffian duct until the latter is close 

 to the cloaca. This is a step in the direction of separating the 

 genital from the excretory ducts, which would be effected if 

 the ducts from the purely excretory part of the kidney were to 

 move still farther down the Wolffian duct and eventually open 

 directly into the cloaca. 



In the female, the Wolffian ducts are solely excretory in 

 function, and the Miillerian ducts or oviducts, which open 

 into the coelomic cavity anteriorly, receive the eggs and convey 

 them down to the cloaca into which they open separately. 



The kidneys retain their open ciliated funnels, leading into 

 the coelomic cavity (ccelomostomes). 



Nervous System. — The brain has large elongated cerebral 

 hemispheres, in the roof of which nerve-cells appear. The 

 floor and side of the hemispheres form the corpus striatum. 

 The cavities of these hemispheres (ist and 2nd ventricles) 

 communicate with that of the diencephalon (3rd ventricle) by 

 the foramina of Monro. The pineal projects upwards from 

 the roof, and the infundibulum down from the floor of the 

 diencephalon ; and a choroid plexus projects into the 3rd 

 ventricle. There is no saccus vasculosus. The roof of the 

 midbrain forms the optic lobes which are joined in the middle 

 line, and do not present a double appearance. The hind brain 

 has a cerebellum and a choroid plexus projecting into the 4th 

 ventricle. 



The cranial nerves are similar to those of the dogfish, 

 except for the fact that the disappearance of the lateral-line 

 organs (or their very great reduction) entails the disappearance 

 of those nerves which supply them, viz. superficial ophthalmic, 

 buccal and mandibularis externus of the facial, and lateralis 

 of the vagus. There is a further simplification owing to the 

 closure of the gill-slits. The glossopharyngeal is distributed 

 to the tongue and pharynx. The vagus supplies the muscles 

 of the larynx, and also sends parasympathetic fibres to the heart, 

 stomach, and intestine. The hypoglossal comes out behind 



