436 wT aa 
extracted from the yolk-sac, the latter is absorbed, and the young fish begins to. 
feed for itself. At the end of three months the adult form is attained, the fish — 
being then hardly an inch in length. a 
The length of time which the hatching process takes, and the rapidity with — 
which the developmental process runs vary much in different species of Telsosts, — 
and is largely dependent on the temperature of the water, spawn deposited in — 
Le, 
Sse eer Peele 
Ms hk (777 CoO pp OL Ss 
Sra EES 
. Bis =| = me $ i 
meee 
me # o\W\ te 
oS are .¢ SACD, 
sents ape) Taney itt CE 
= masse Sate 2 2 6794) 
ry . bd eo? He 
o 3 eiges fe o 40 
eve Pi * Ce 
. 
RICHER Verge) OB i are kart 
. . 
. eo te 
. eS ea 
at 7 “e5 
. +. ° y 5 
5 : I eee . 
q Pi pe 
~ - eT wien 
ero ee ofl 168, 88 
Fig. 8.—DIAGRAM OF SEVERAL STAGES IN DEVELOPMENT OF OaTvISH. (Modified from Ryder). 
1, ovarian egg ; 2, egg in which formative yoke has separated to upper pole ; 3, embryo of second day ; 
4%, section through such an embryo, showing epiblast with nervous system above, hypoblast below, and — 
between thera the mesoblast and the notochord ; 5 embryo of sixth day. 
the cold water of October and November not hatching till the following spring 
in contrast with the rapid process depicted above, which occurs in the early sum- 
mer. The great difference in size which is to be observed between the egys of — 
different species is not merely proportional to the size of the species, although, as 
we shall find, large varieties of brook trout lay larger eg ss than small varieties ; 1b 
is largely a question of the relative am unt of food-yolk provided for the embryo, 
and may be therefore also attributed to the hatching habit of the species, the — 
longer or shorter time which the embryo takes to burst the egg-shell and to begin — 
to feed for itself. | 
The following table gives the number of egzs that have been counted to” 
a quart in different species :— 
Mide@learal. ©. 7 isece o)c. scien aia: wre svat ee 1,267,728° 
Pickerel (Stizostediwm vitrewm)................ 120,000 
aVihtibatisk® . 7“Senides; 2% 3G os sede (655 eee eee 36,000 
Striped, Mass Fey ys 2) tok) i. es ae 24,363 
Brook WeoGgh «este iss. Se etek ee oe 11,000 
Dele Prone oc ee as re eo Se 8,720 
Miantic Malmo wei as ba oe ee 4,272 
Winning sas Oh as wite oh, dsc ata ee 3,000 
