278 



LUNG-FISHES 



x, 6 



16 



A further amphibian feature of the blood-vascular system is the 



presence of an inferior vena cava, a 

 vessel collecting blood from the kidneys 

 and reaching to the heart by passing 

 round to the right of the gut in the 

 mesentery. The more dorsal cardinal 

 veins, joining the ductus Cuvieri, remain 

 present, however, and there is a renal 

 portal system. 



The adrenals of Dipnoi are represented 

 by two separate masses of tissue. The 

 perirenal tissue of Protopterus is a con- 

 siderable mass of material around the 

 kidney, containing lipid, steroid, and 

 round-cell (lymphoid) tissues, as well 

 as endothelial and pigment cells. The 

 steroid tissue shows histochemical pro- 

 perties similar to those of mammalian 

 adrenal cortex and undergoes changes 

 after injection of mammalian ACTH. 

 This tissue thus shows a collection of 

 functions, haematopoietic, phagocytic, 

 storage, endocrine, and pigmentary, 

 which may show the starting point of 

 the evolution of the tetrapod adrenal 

 cortex. Cells that give the chrome 

 reaction, the adrenal medullary tissue, lie 

 in the walls of the intercostal branches 

 of the dorsal aorta. This condition could 

 have given rise to that of amphibia. 



The arrangement of the urinogenital 

 system is similar to that of amphibia and 

 is probably closer to that of the ancestral 

 gnathostome than in any living elasmo- 

 branch or actinopterygian. In the male 

 there are vasa efFerentia by which sperms 

 are passed through the excretory portion 

 of the mesonephros. In the female eggs 

 are shed free into the coelom and carried 

 out by a Mullerian duct, whose opening lies far forward. An in- 

 teresting feature is that the Mullerian duct is very well developed in 





— 1 



Fig. 168. Dorsal view of the brain 

 of Protopterus. 



I, spinal cord; 2, dorsal root of first 

 spinal nerve; 3, diverticula of 4, the 

 saccus endolyinphaticus; 5, medulla 

 oblongata; 6, fourth ventricle; 7, 

 cerebellum; 8, mesencephalon (fused 

 optic lobes); 9, stalk of pineal body; 

 10, thalamencephalon; 11, velum 

 transversum; 12, pineal body; 13, 

 lobushippocampi; i4,choroidplexus ; 

 15, cerebral hemisphere; 16, olfac- 

 tory lobe. (After Burckhardt, from 

 Goodrich.) 



