25() 



DIPNOI. 



Urinogenital Organs. The kidneys* are without nephro- 

 stomata ia the adult ; they are elongated glands not differentiated 

 into meso- and meta-nephros. Each of thera has a ureter which 

 either joins its fellow before opening into the cloaca (Ceratodus) 

 or the ureters open separately into a cloacal caecum 

 derived in development from the fused hind ends of 

 the longitudinal ducts. The larva possesses a pro- 

 nephros on the Amphibian type with two funnels and an 

 elongated glomeriilus contained in an incompletely separated off 

 portion of the body-cavity. The ovaries and testes are elongated 

 bodies. The oviducts are convoluted tubes opening anteriorly 

 and far forward into the body cavity and joining behind to open 

 into the cloaca just in front of the ureters. The testis has a 



Fig. 133.— Longitudinal vertical section through tlie brain of P/o<o/)<«rM« (after Burckhardt). 

 1 choroid plexus of 4th ventricle ; 2 cerebellum ; •} mesencephalon ; 4 posterior com- 

 missure ; 6 pineal stalk ; 6 superior commissure ; 7' velum transversum ; S pineal body ; 

 9 choroid plexus ; 10 corpus callosum ; 11 anterior commissure ; 13 optic chiasma ; 13 

 saccus vasculosus ; 14 pituitary body ; Id spinal cord. 



longitudinal duct extending along its whole course. This duct 

 communicates with the tubuli seminiferi on the one hand and by 

 a number of transverse tubes with the hinder part of the kidney. 

 It ends blindly in front and behind, and has been fully made out 

 in Lepidosiren ; it probably exists in Ceratodus. A similar duct 

 is described by Parker in Protoptems, where it is said to open 

 into the cloaca and not to communicate by transverse tubes 

 with the kidney. This is however denied by Kerr. The mak^ 

 possesses a well-marked vestige of the oviduct. 



The egg is of considerable size and undersoes complete unequal 

 cleavage. The early development is very like that of Amphibia 



* Kerr, Proc. Zool. Soc. 1901, p. 484. 



