THE REARING OF SEA-FISH LARV^. 75 



occupied 15 or 16 seconds, followed by a pause of 5 seconds, but 

 the upward stroke was smarter and lasted only 8 seconds. The 

 apparatus was then quiescent for about 12 seconds before the next 

 stroke began. The eddies in the water caused by the rapid move- 

 ments of the plunger were so extensive that the larvas were frequently 

 caught in the streams and whirled around, and, although these involun- 

 tary gyrations did not appear at the time to have any greater effect 

 than to temporarily arrest the activity of the larvte, I was soon con- 

 vinced that the mortality which the larvae exhibited in these first 

 experiments was largely attributable to the incessant harrying to which 

 the movements of the plunger subjected them. When the original 

 plunger-plate was replaced by a much smaller one of 2^ inches diameter, 

 not only were the water-movements greatly moderated, but the condition 

 of the larvffi generally improved. 



The powers of the larvae in stemming a constant current, however, 

 were considerable. When the water in a jar was being changed, the 

 waste water was at first siphoned off through a glass tube provided 

 with a thistle-funnel (covered with fine gauze) at one end and a stop- 

 cock at the other. It was remarkable to notice the success with which 

 both Copepods and young Blenny larvre could for some time compete 

 with the current setting through the funnel, even when the tap was 

 fully open. As soon as they felt themselves within the influence of the 

 current they would give vigorous darts in the opposite direction, the 

 fishes generally escaping, the Copepods often. But the weaker larvae 

 which did not dart away smartly enough were drawn up against the 

 gauze. The weakest would remain there, scarcely offeriug resistance ; 

 but the majority, as soon as they touched the tight gauze surface, would 

 give a most powerful leap, and dart clear away from funnel and current 

 alike into relatively still water. Many showed no serious objection to 

 the current itself, and allowed themselves to be drifted up against the 

 gauze ; but the moment they felt this obstacle they leaped away as just 

 described. The Copepods, as a rule, were unable to jerk themselves 

 beyond the influence of the current except momentarily, and thus 

 maintained a prolonged contest in the form of incessant darts or leaps 

 from the neighbourhood of the sieve, to be repeated as fast as the 

 current beat them back upon it. 



Experiments A, B, and C. 

 The experiments which I made last year fall into four groups (see 

 table p. 76). The first set (A, B, and C) was designed to test the effect 

 of confining the young larvre in jars of water fitted with Browne's 

 stirring* apparatus known as the "plunger." Three jars of the same 

 size and shape were employed, and were fitted with plungers of equal 



* See Journ. M. B. J., v., 1898, p. 176. 



