432 ON THE ANATOMY OF POLYPTERUS. [May 8, 



With increase in size of the ova, the external wall bulges out 

 into great folds between the septa, while the internal wall remains 

 a smooth sheet of peritoneum. As the ova develop, they become 

 deeply pigmented upon the pole of the ovum, which is attached to 

 the original outer wall of the ovary. It thus comes about that 

 when ripe, through the smooth internal wall of the ovary only the 

 colourless poles are seen, while through the external much-folded 

 wall only the pigmented poles are seen. It has been stated that 

 the outer wall of the ovary of Polypterus is without a covering of 

 peritoneum ; it will be seen from the description that this is not 

 strictly correct. 



General considerations on the Structure and Growth of the Urino- 

 genital Organs. — I have shown that in the male Polypterus there 

 are no connections between the testis and the kidney by which 

 the latter could carry off the products of the testis, as is the 

 case in Lepidosteus and perhaps some other Ganoids. 



I have shown also that the arrangement of the ducts of the 

 genital glands is very similar in male and female, and that in 

 the larva this resemblance amounts almost to identity. From the 

 early development of these ducts, and the similarity in the male 

 and female, I regard the condition found in Polypterus as the 

 primitive arrangement ; and that in all cases where connections 

 are found between the testis-tubules and the tubules of the 

 kidney, they are either inherited along a divergent line of ascent, 

 or, as in the case of Lepidosteus, secondarily acquired. 



Abdominal Pores. — In both male and female, abdominal pores 

 are present in Polypterus. These pores are acquired late in life, 

 after the Polypterus is 9 cm. in length. 



Anal Fin. — Traquair has already noted in Calamoichthys that 

 the males have an enlarged anal fin. This difference is, in the 

 breeding-season, one also of form as well as size. The anal-fin 

 muscle in the male increases in size so much that the viscera in 

 the posterior end of the coelom are displaced. Fertilization is 

 probably not internal, as has been suggested by Leydig. 



External Gill. — The structure of the external gills is precisely 

 that of larval Dipnoi and Amphibia. 



Hyrtl supposed the external gill of Polypterus to be homologous 

 with the endodermal pseudobranch of Acipenser. From a study 

 of the blood-supply, I conclude that it is rather homologous 

 with the external ectodermal gill of larval Dipnoi and Amphibia, 

 which have properly an external and an internal gill to each visceral 

 arch. 



Vascular System. — In this preliminary abstract of my paper, I 

 will merely state that my investigations lead me to agree with 

 Pollard in regarding the arterial system of Polypterus as only 

 comparable with the primitive Chlamydoselachus and embryo 

 Selachians, where from each gill-arch a single efferent vessel unites 

 with a median precardial aorta. 



Cranium.— 1 find that there is an important specific difference 

 in the form of the sphenoid of the two species P. seneyalus and 



