NOTES ON TELEOSTEAN OVA AND LARVAE. 37 



black pigment into two groups, the first a short distance behind the 

 anus, usually confined to the ventral half of the body, the second in the 

 form of a band from the dorsal to the ventral contour, besides which 

 there is, in the hypural region, a small patch of pigment which has out- 

 growths to the marginal fin. 0. cimbrius shows only one of these 

 post-anal pigment groups. 



O710S mustela, L. 



To come to tlie consideration of my own specimens, they 

 can with very little exception be designated Onos mustela. There 

 is, of course, the bare possibility that the eggs and larvae of some 

 other species of rockling, which are at present unknown, may so 

 closely resemble those of 0. mustela as to have been indistinguishable 

 from them by me. But even if such were the case, the number so 

 included would be quite inappreciable against the total, which are 

 undoubtedly 0. mustela. These eggs occurred in my tow-net and 

 young-fish trawl plankton samj)les from 11th February to 25th 

 June, and again in August and September. The diameter varied from 

 072 to 0-83 mm., averaging 0-77 for February to March, 0-78 for April, 

 and 0'72 for May to June. The diameter of the oil-globule varied from 

 0"13 to 018 mm. It sometimes happened that the size of the oil- 

 globule was the reverse of being proportional to the size of the egg, 

 i.e. the larger eggs of a sample had the smaller oil-globules, which 

 I thought might possibly be significant of a specific difference, but 

 observations of the resulting larvae disproved this. The oil-globule, 

 which may be subdivided into two or three in the early stages, com- 

 monly has a more or less greenish and sometimes a cupreous tint. 

 The yolk surface is somewhat corrugated. By the time the embryo 

 has developed a caudal rudiment, small black chromatophores appear 

 generally in a double line along the body, on the head, and in the 

 pellicle of the oil-globule. They soon increase in size, and may become 

 stellate, especially the anterior ones. Just before hatching the two 

 characteristic post-anal groups (or " zones ") of pigment are generally 

 quite distinct. One of my smallest newly hatched larvae measured 

 1*88 mm. (the pre-anal length being 076 mm.), and the largest size 

 I have recorded for this stage is 2*32 mm. The black pigment, which 

 is mostly stellate and dendritic, is distributed upon the head, in the 

 peritoneum, over oil-globule, laterally on the trunk over the anus, 

 in the two large distinct post-anal groups above mentioned, and in the 

 hypural region. These groups or zones are formed by the occurrence 

 of short dorsal and ventral bars of black pigment spots, more or less 

 fused together, from which dendritic outgrowths extend laterally. 

 Sometimes such a bar may consist of only two or even one large 



