xin 



PHYLUM CHORDATA 



251 



epibranchial arteries into a single lateral trunk. In Protopterus 

 there is usually a single abdominal pore opening on the dorsal wall 

 of the cloaca ; this leads into a cavity into which the true abdominal 

 pores, which are very minute, 

 lead. In Lepidosiren abdominal 

 pores are absent. 



The brain in both Lepidosiren 

 and Protopterus, as well as in 

 Ceratodus, differs from that of 

 Fishes in general, and resembles 

 that of Amphibia (see Section 

 XIV) in the presence of long and 

 relatively narrow cerebral hemi- 

 spheres. In the two former 

 these have a pallium or nervous 

 roof with a stratified layer of 

 nerve-cells. In all the Dipnoi 

 the part of the hemisphere (ol- 

 factory lobe and tuberculum) 

 from which the olfactory nerve- 

 fibres pass to the bulbus ol- 

 factorius is of relatively large 

 size, but smaller in Protopterus 

 and Lepidosiren. In Protopterus 

 and Lepidosiren the olfactory 

 tract is not distinguishable, 

 bulbus and lobus being in im- 

 mediate apposition instead of 

 being widely separated as they 

 are in Ceratodus. In both these 

 genera the dorsal part of the 

 mid-brain is undivided. In 

 both genera the kidneys are re- 

 latively more elongated than in 

 Ceratodus ; in Protopterus the 

 posterior portions are fused 

 together ; in Lepidosiren they 

 remain separate throughout. 

 In both genera the elongated 

 testes are distinguishable into 

 two regions an anterior longer, 

 sperm-producing part, and a 

 posterior shorter part which serves as a duct and a vesicula semi- 

 nalis. In Lepidosiren about six vasa efferentia arise from this 

 posterior region and enter the Malpighian capsules of the meso- 

 nephros : in Protopterus there is only a single vas eSerens. The 

 ducts of the two kidneys open by a single aperture (Protopterus) 



