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Show 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 seem 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 Urinogenital 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 Lepiclosteus 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 aud 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 tbe viscera in the posterior end of the ccelom 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 m y paper, I will merely state that my investigations lead m e to agree with Pollard in regarding the arterial system of Polypterus as only comparable with the primitive Chlamgdoselachus and embryo Selachians, where from each gill-arch a single efferent vessel unites with a median precordial aorta. Cranium.-I find that there is an important specific difference in the form of the sphenoid of the two species P. senegcdus and |
