564 W, N. F. WOODLAND. 



oval area would be shut off from the general bladder cavity in the 

 same way that the cavity of the posterior chamber is shut off from 

 the anterior in the Carp bladder. My investigations prove that this 

 last anticipation is correct in the case of the ovals of tlie two fish 

 (Pollack and Mullet) which I have examined. As shown by Figs. 5 

 and 6, the oval in the Pollack opens and closes by means of a circular 

 fold which works like the shutter of an iris diaphragm. The im- 

 permeable inner layer of the bladder wall is shown by a thick line, 

 and, as the figures indicate, this ceases at the edge of the open oval, 

 the oval area merely being covered by the thin layer of squamous 

 epithelium. As the figures also indicate, the circular fold is formed 

 by the actual rotation of the tissue round the edge, hence the more 

 closely shut the oval the deeper is its cavity. This deep cavity of the 

 closed or nearly closed oval is very obvious in the actual bladders 

 of the Pollack, Mullet, and other fish, but, according to the statements 

 of Nusbaum and Eeis, it does not exist in the species they examined. 

 I am, of course, quite ready to admit that all ovals may not work on the 

 same principle — in Dadyloptervs volitans, e.g., T find that the oval-like 

 structure has in section an appearance different in several particulars 

 from that of the normal oval; at the same time, I shall feel more 

 satisfied that the mode of action of the oval in Perca, Lucioperca, and 

 Ophidium is different from that of the oval of Gadus, Mugil, and 

 other fish, if Nusbaum and Eeis would supply us with figures con- 

 structed from observations of actual sections of the open and closed 

 oval instead of mere diagrams which, to say the least, look very 

 hypothetical. The figure of the open oval of Lucioperca published by 

 Reis (Krakow, Eozpr. Akad., 1906, pp. 639-670) is of little use as 

 evidence in the present connection. 



I must point out, in conclusion, that, literature being not easily 

 accessible in the centre of India, papers bearing upon the above subject 

 may have been published without my knowledge since I left University 

 College, London. I must also confess that I am unacquainted with the 

 exact nature of the controversy concerning the oval between Nusbaum 

 and Jaeger. Possibly Jaeger has already stated the objections I liave 

 urged above. If so, he has not confirmed them with figures. Finally, 

 I may mention that I have exhibited my own sections of the open and 

 closed oval at the Pioyal Institution of London, where they were 

 examined by several zoologists of repute. 



