SEA-FISHERIES LABORATORY. 339 



On spawning a very marked change takes place. 

 Fig. 21 represents the condition of a mature and spent 

 female. The ovary is seen to be considerably retracted, 

 and is only just visible on opening the body cavity. Its 

 walls are soft and flaccid, and enclose a large cavity. The 

 posterior extension still exists, and is indeed not much 

 shorter than in the ripe specimen. The condition of the 

 fish is indicated externally by a shallow groove running 

 backwards on either side in the position formerly occupied 

 by the pad spoken of above. The flesh is lean, and the 

 fish is generally regarded as in poor condition as a food. 



It appears* that after spawning the ovary never 

 reverts to its former immature condition. That is, it is 

 always possible to distinguish between a spent mature, 

 and an immature fish. Similar contrasts are exhibited 

 by the various phases of the testes, but on account of the 

 relatively small volume of these organs the changes are 

 not so striking and afford no external indications. 



The ovary of the Plaice, like that of the majority of 

 Teleostean fishes is a sac the wall of which is continuous 

 with that of the oviduct. This is the cystoarian condition, 

 and for an understanding of the morphology of such an 

 ovary the other common type met with among Teleostei, 

 the elasmoarian ovary, must be studied. f The internal 

 wall of the cystoarian ovary corresponds to the external 

 face of the peritoneal lamella which forms the elasmoarian 

 organ, and to the outer visible surface of the ovary of an 

 Elasmobranch fish — the surface from which the ova 

 dehisce into the general body cavity. There can be no 

 doubt from the work of Balfour and Parker 1 on Lepi- 

 dosteus, that the cavity of the cystoarian ovary into which 



* See Holt, Joum. Mar. Biol. Ass., vol. ii., p. 363. 



f See Howes — Hermaphrodite genitalia of the codfish. Jour. Linn. 

 Soc, London, vol. xxiii., 1891, pp. 539-557. 



I Structure and development of Lepidosteus, Phil. Trans., vol. clxxiii., 

 Part 2, 1882. 



