426 THE HERRING FAMILY. 



little to note concerning the development within the egg, which 

 conforms closely to the clupeoid type. Cunningham found an 

 interesting example of a pilchard's egg which had a very much 

 reduced perivitelline space, in fact no larger than in the normal 

 sprat's egg. The embryo within hatched successfully and 

 appeared perfectly normal, although developing under such 

 abnormal conditions. Variations such as this may possibly be 

 explained as atavistic, and would in this case point to the 

 conclusion that a large perivitelline space has been secondarily 

 acquired from an earlier type of egg with a small space of this 

 nature. 



Plate XIX, fig. 1, gives the appearance presented by the 

 larva upon hatching ; the very sparse supply of pigment, the 

 sub-terminal position of the vent, and the unicolumnar notochord 

 are all clupeoid characters. The yolk-sac is large, with the oil- 

 globule still persisting at its hind region ; the vesicular nature 

 of the yolk is marked. Cunningham gives the length of the 

 newly hatched larva as 3'8 mm., and he also mentions an entire 

 absence of pigment, which however does not appear to be 

 general, for Raffaele describes and figures sparsely distributed 

 black spots on the head and trunk, and later the former observer 

 has found ' a few black chromatophores along the dorsal region 

 of the body.' In an entire absence of pigment in the eyes 

 immediately after hatching the pilchard agrees with the sprat, 

 but contrary to a statement by Cunningham, disagrees with 

 the herring, which upon emerging from its demersal egg has 

 deeply pigmented eyes (Kupffer, Brook, etc.). 



These larvse referred to were hatched by Cunningham at 

 Plymouth Laboratory in September. The temperature of the 

 tanks being about 17 C., the period of incubation was shortened 

 to three days. They agree with those quoted above from 

 Raffaele's observations. When hatched there is no external 

 opening of the mouth, the head being depressed upon the 

 yolk-sac. About the third day after hatching the mouth is 

 open and owing to the elongation of the lower jaw it soon 

 assumes a terminal position. At this date the eyes which 

 hitherto had been colourless presented a little yellow pigment 

 and 'reflecting substance.' On the day after this, viz., the 



