508 



DIPNOI 



[CH. 



-to 



along the testis which acts as a collecting 

 duct. A quite similar arrangement is 

 found in the lower Amphibia as well (as 

 already described) as in Chondrichthyes. 



In Lepidosiren the hinder part of the 

 testis is sterile and consists mainly of this 

 longitudinal duct with some rudimentary 

 tubules, and this portion alone is con- 

 nected with the kidney by five or six vasa 

 efferentia. 



Finally, in Protopterus there is the 

 same sterile extension of the testis, and 

 this is connected with the kidney by a 

 single vas efFerens which joins the neck 

 of the capsule of one of the kidney 

 tubules. If vas efFerens and tubules were 

 simplified into a single wide tube we 

 should reach the condition of Polypte- 

 rus, and if this duct were split off from 

 the archinephric duct and acquired a dis- 

 tinct opening to the exterior, we should 

 reach the condition of Teleostei. 



The alimentary canal has a spiral 

 valve, as in other archaic groups of fish. 

 The brain of Protopterus and Lepido- 

 siren resembles that of Chondrichthyes 

 and Amphibia in having definite cerebral 

 hemispheres with nervous matter all 

 round, but that of Ceratodus is like the 

 brain of Osteichthyes in having only a 

 membranous roof. The opening of the 

 nasal sac is divided into two as in almost 

 all Osteichthyes, but the whole sac lies, as 

 in Chondrichthyes, on the under side of 

 the snout, and the inner opening is within 

 the stomodaeum, thus foreshadowing 

 FIG. 249. Lateral view of the skeleton of Ceratodus mlolepis. After Giinther. 



1, 2, 3. Boofing membrane bones. 4. Cartilaginous posterior part of cranium. 

 5. Pre-opercular (squamosal). 6. Opercular. 7. Suborbital. 



8. Orbit. 9. Pectoral girdle. 10. Proximal cartilage of pectoral fin. 

 11. Pectoral fin. 12. Pelvic girdle. 13. Pelvic fin. 14. Spinal 

 column. 15. Caudal fin (diphycercal). 



vm 



or' 



