298 ME. G. BROOK OK SOME POINTS TK 



DESCRIPTION OF PLATE VII, 



Fig. 1. Heterolepidotus grandis, Dayis, one third nat, size. 



Fig. 2. Scales, natural size. 



Fig. 3. Anterior fin-ray of the pectoral fin, natural size. 



On some Points in the Development of Motella mustela, L. 



By G-EOE&E Begoe, P.L.S. 



[Read 6th November, 1884.] 



(Plates VIII.-X.) 



The eggs of M. mustela which I have been enabled to study 

 were deposited in my aquarium during the months of May and 

 June. They belong to the pelagic group of Teleostean eggs, and 

 have usually one large oil-globule which keeps them floating on 

 the surface of the water, although in a few cases I have found a 

 cluster of from two to eight, or even more. These, however, 

 were abnormal forms. Dr. Day, in his ' Fishes of G-reat Britain 

 and Ireland,' i. p. 315, quotes from the ' Zoologist,' 1879, p. 476, 

 the following words of Cornish : — " The nest wherein the spawn 

 is deposited is invariably formed of the Common Coralline, 

 Oorallina officinalis, thrust into some cavity or crevice of a rock 

 close to low-water mark." There must surely be some error 

 in this observation, as it is manifestly entirely contrary to the 

 nature of a pelagic egg to be retained in a nest. The eggs of 

 all the other Gradidse, so far as known, are pelagic, so that there 

 is nothing exceptional in those of Motella being so. 



The eggs are somewhat oval in shape, and are not all of equal 

 size. The length of the longer axis varies from "655 millim. to 

 •731 millim., and that of the shorter axis from 'BiO millim. to 

 •716 millim. The shape, however, seems to vary considerably. 

 Many are almost globular ; and the oval shape seems often to be 

 produced by three or four eggs touching one another. The 

 slightest pressure alters the shape of the egg in this species, a 

 feature which I have never observed in the egg of Trachinus. 

 In normal eggs the siuale oil-globule is usually about '11 millim. 

 in diameter. In those eggs with more than one oil-globule there 

 is usually about the same volume of oil as in the large single 

 globule, but divided into larger or smaller globules, according 

 to the number. A batch of eggs which were laid on the 28th of 

 May had the majority of the eggs with more than one oil-globule, 



