THE ANATOMY OF POLYPTERUS. 327 



The ovary in Polypterus develops as a genital ridge lying along the ventral surface 

 of the kidney, and separated from it posteriorly by the genital duct (PI. LII. figs. 21, 

 22, 23). 



A large vein and artery traverse the median wall of the ovary (PI. LII. fig. 21, b.v.). 

 The ovary becomes divided into numerous compartments, on the outer wall of which the 

 ova are developed (PI. LII. fig. 21, o.at., and text-fig. 1, p. 326). 



With increased development of the ova in size and number, the outer wall becomes 

 greatly enlarged in surface, while the median wall is not thus enlarged (text-fig. 2). 

 It thus happens that the outer wall bulges out into great folds between the septa 

 (text-fig. 3). 



As the ova develop they become deeply pigmented upon the pole of the ovum 

 which is attached to the outer wall of the ovary. Although the outer wall becomes so 

 much folded, nevertheless the ova retain their original " orientation " at the extremities 

 of each fold, so that, when ripe, through the median wall of the ovary, which is 

 a thin smooth sheet, only the pigmentless poles are seen (text-fig. 3, o'), while 



Fig. 4. 



cat 



The ovarian ovum of Polypterus, with attachment (o.at.) 

 to the outer wall of a compartment of the ovary. 



through the external much-folded wall only the pigmented poles are seen (text- 

 fig. 3, o"). It has been stated that the outer wall of the ovary of Polypterus is without 

 a covering of peritoneum. It will be understood from the above-given description 

 of the growth of the ovary, and from the examination of text-fig. 4, that this is not 

 strictly correct. 



IV. The Kidneys. 



The kidneys are similar in male and female. They consist of two bands of excretory 

 tubules, glomeruli, and embedding lymphoid tissue (PI. LI. figs. 10, 11, 16) lying on 

 either side of the vertebral column between the peritoneum and the muscles of the 

 body-wall, and are constricted metamerically by the projecting myocommata. The 

 kidneys of the two sides do not unite (PI. L. figs. 2, 3, Jc.). 



The minute structure of the kidney of the young Calamoichthys has been described 

 by Lebedinsky. His description of the arrangement of the tubules in Calamoichthys 



