THE BLENNY FAMILY. 203 



An epitome of the main differences is here given : 

 Larva of Wolf -fish. Larva of Salmon. 



1. Yolk and contained oil-glo- Yolk of reddish orange colour, 

 bale of inconspicuous colour, and from contained oil-globules, and 

 yolk-sac spheroidal. elongated in outline. 



2. Single large oil-globule an- Many small oil-globules situated 

 terior in position. in upper part of yolk-sac. 



3. Snout very blunt, so that Snout protrudes well in front of 

 the eyes are the most anterior part the eyes. 



of the head. 



4. Marginal fin continuous. Marginal fin with interrupted 



outline, forming separate median 

 fins. 



These leading features will at once serve to separate the two 

 species at the larval stage. 



The blood-vessels in the yolk-sac are, as already indicated, 

 remarkably developed ; and a minute account of the changes 

 undergone by them during later development will be found else- 

 where 1 . A comparison of these and other organs in the wolf- 

 fish and the salmon show that the stages presented by the 

 former after hatching are passed through by the latter in the 

 egg, so that the young salmon hatches at a stage more re- 

 sembling the adult, in this respect being further removed from 

 the type of development presented by the pelagic larvae of the 

 gadoids and pleuronectids. We may here state that the fact 

 that the young salmon only hatches at a comparatively late 

 stage of development, compared with marine Teleosteans, is in 

 accordance with the generalisation that all animals having a 

 fresh water habitat tend to acquire a much modified and 

 protected form of development. This is no doubt a direct 

 adaptation to their more precarious surroundings : the numerous 

 vicissitudes and dangers of our streams and rivers, compared 

 with the sea as a nursery, are obvious. 



The absorption of the yolk is slow, and the larval period 

 may thus continue till the end of June, but may terminate in 

 some cases at the middle of May. 



Upon hatching, the larva is of a dull yellow translucent 

 colour, with a few black stellate pigment-spots upon the head, 



1 Op. cit. 



