THE HERRING. 443 



eight days ; the average being seven days. And this is a very inter- 

 esting fact when we bear in mind the conclusion to which the inquiries 

 of the Dutch meteorologists, and, more lately, those of the Scottish 

 Meteorological Society, appear to tend, namely, that the shoals prefer 

 water of about 55. At 50 Fahr., the period of incubation is length- 

 ened to eleven days ; at 46 to fifteen days ; and at 38 it lasts forty 

 days. As the Forth is usually tolerably cool in the month of March, 

 it is probable that Professor AUman's estimate comes very near the 

 truth for the particular case which he investigated. 



The young, when they emerge from the ^g^, are from one fifth to 

 one third of an inch in length, and so extremely unlike the adult 

 herring that they may properly be termed larvae. They have enormous 

 eyes, and an exceedingly slender body, with a yelk-bag protruding 

 from its fore-part. The skeleton is in a very rudimentary condition ; 

 there are no ventral fins ; and, instead of separate dorsal, caudal, and 

 anal fins, there is one continuous fin, extending from the head along 

 the back, round the tail and then forward to the yelk-bag. The intes- 

 tine is a simple tube, ciliated internally ; there is no air-bladder, and 

 no branchiae are yet developed. The heart is a mere contractile vessel, 

 and the blood is a clear fluid without corpuscles. At first the larvae 

 do not feed, but merely grow at the expense of the yelk, which gradu- 

 ally diminishes. 



Within three or four days after hatching, the length has increased 

 by about half the original dimensions, the yelk has disappeared, the 

 cartilaginous skeleton appears, and the heart becomes divided into its 

 chambers ; but the young fish attains nearly double its first length 

 before blood-corpuscles are visible. 



By the time the larva is two thirds of an inch long (a length which 

 it attains one month after hatching), the primitive median fin is sepa- 

 rated into dorsal, caudal, and anal divisions, but the ventral fins have not 

 appeared. About this period the young animal begins to feed on small 

 Crustacea ; and it grows so rapidly that, at two months, it is one and a 

 quarter inch long, and, at three months, has attained a length of about 

 two inches. 



Nearly up to this stage, the elongated, scaleless little fish retains 

 its larval proportions ; but, in the latter part of the third month, the 

 body rapidly deepens, the scales begins to appear, and the larva passes 

 into the "imago" state that is, assumes the forms and proportions 

 of the adult, though it is not more than two inches long. After this, 

 it goes on growing at the same rate (eleven millimetres, or nearly 

 half an inch) per month, so that, at six months old, it is as large as a 

 moderate-sized sprat. 



The well-known "whitebait" of the Thames consists, so far as I 

 have seen, almost exclusively of herrings, under six months old, and as 

 the average size of whitebait increases, from March and April onward, 

 until they become suspiciously like sprats in the late summer, it may 



