74 PRELIMINARY EXPERIMENTS ON 



3 to 4 hours old. 20 to 24 hours. 



Total length . . . . 4-6 4-5 4'6 ... 4-6 



Length from anterior extremity to ) , ,g ,,^ , ,„ ,.,^ 



posterior surface of yolk . . j 



Ditto to posterior surface of rectum . 1'62 1'55 1'58 ... 1'60 



These larvie were hatched on August 4th from a batch of eggs 

 dredged the same day. They were killed and preserved in weak 

 formalin, and measured on August 5th. In view of the slight nature 

 of the differences in my measurements of separate individuals, it is 

 difficult to account for the discrepancy * between our observations, 

 especially as I find the same length in early larvre of another batch 

 hatched on June IGth. The difference can scarcely be attributed to 

 contraction of my specimens in formalin, since in the oldest of the 

 above-mentioned larvse the longest rays of the pectoral fin were seen to 

 fall short of the anus by 0'15 mm., whereas in Holt's specimen they 

 extended 0-12 mm. behind the anus. Moreover, in larvae which had 

 died a natural death and become opaque, the pectoral fin-rays were 

 often noticed to stretch beyond the anus, as in Holt's specimen, but this 

 was never the case with fresh or living larvai derived from the August 

 batch referred to above. Several larvae measured fresh on the third and 

 fourth days had a length of exactly 5 mm. 



Holt remarks upon the delicacy of the larvae and their susceptibilities 

 to slight injuries, an observation which in the early stages of these 

 experiments I had frequent opportunities of confirming. The water in 

 the jars was at first renewed by siphoning off half the water and 

 pouring slowly from a broad-lipped jug, at first directly and subse- 

 quently through a funnel ; but the currents produced by the first 

 method, and the impact of the bubbles of air driven down the funnel, 

 were excessive and caused considerable injury. This method was sub- 

 sequently replaced by allowing the water to enter the jars in a slow 

 stream from a siphon provided with a stopcock. Even the capture of 

 a larva by means of a dipping tube was sufficient to stun and kill it. 



If the larvae are kept in a " plunger-jar," the diameter of the plunger- 

 plate in relation to the diameter of the jar is an important item, and 

 any excess which produces eddies of any violence during the move- 

 ments of the plunger is certain to prove fatal. At first my larvae were 

 placed in tall bell-shaped hatching jars having a height of 16 inches 

 and an internal diameter of 8 inches. The plunger-plate was circular 

 and had a diameter of 4i inches. The plunger made three complete 

 strokes in exactly two minutes, i.e. one plunge, including both down 

 and up stroke, in 40 seconds. The downward stroke was gentle and 



* Mr. Holt informs me by letter that the total length assigned to the larva in his papers 

 is a mistake due to an error of transcription, and should have been 5 '30 mm. After a re- 

 examination of his specimens, however, I find the total length to be the same as in mine, 

 viz. 4"6 mm. (varying between 4'55 and 4*65). I have verified the accuracy of my micro- 

 meter, 80 that no ditrereuoe between our larvae ueed be assumed. 



I 



