224 



Part III. — Sixteenth Annual Repm^t 



" bite " of food was taken. The two ways of nourishing are more likely 

 to intermix — that a certain amount of food is eaten while yolk is still 

 present. And if this is the natural process in regard to young plaice, it 

 is not surprising that early feeding cannot successfully be dispensed with. 



"With the view of finding out whether the larval plaice would take any 

 food before the absorption of the yolk w^as completed, I placed some 

 newly-hatched fry in a rearing jar early in May, and added to the water 

 tow-net collections containing samples of the ordinary plankton on this 

 coast. When between three and four days old about the half bulk of the 

 yolk had been absorbed, and the mid-gut had by this time begun to form 

 the sling; this, however, was not nearly completed. At this stage the 

 larvce began to take food. The nature of the latter was much the same 

 as I have found to constitute the food in the early post-larval stage. 

 Small larval molluscs and larval crustaceans were observed in the stomach, 

 though most frequently forms of infusoria {cei'etiam s}).) were observed, 

 and sometimes diatoms. In one specimen which was three days old, and 

 the mid-gut yet quite straight, I found four specimens of ceretium. The 

 fact that the larvse did take food regularly at this early stage makes it 

 very probable that it is natural to them and that they will do so in the 

 open sea generally. Though it does not seem to be an absolute condition 

 for successful development (compare the rearing experiment carried out in 

 1896), there is reason to believe that the percentage of surviving indi- 

 viduals will be much increased by an early feeding. Some further experi- 

 ments may illustrate this more graphically. When transporting plaice 

 fry long distances in 1896 I found that best results were always obtained 

 with those that still had the greater part of the yolk mass unabsorbed. 

 Any relation between this experience and the above-mentioned peculiarity 

 tends to show that the plaice larva has a greater vital resistance in the 

 middle than towards the end of the larval stage in cases when additional 

 nourishment has not been supplied. This very interesting fact in connec- 

 tion with larval plaice has to my knowledge not previously been stated; 

 it will probably form a point of importance in the case of artificial rearing 

 in laboratories, where such experiments as yet have had little success. 



From lemon soles, which had been delayed in their spawning, I obtained 

 some fertilised eggs in September. After hatching, an experiment for 

 rearing of the larvae was arranged and food supplied in the usual way. 

 Soon after the mouth was open they began to eat ; the yolk was then 

 nearly absorbed.* The larvse took food abundantly, but did not seem to 

 thrive on it. 



Tow-net collections were obtained from various places in the locality 

 and were taken near the surface and at greater depths, but the food thus 

 supplied did not seem to agree with them, although it was eaten of freely. 

 Some of the larvse were kept for ten days after the yolk had been 

 absorbed; this was in the beginning of October, and it must be remem- 

 bered that June and July is the usual time for the development of the 

 lemon sole larvse. Seasonal changes in the plankton on the coast would 

 probably be of adverse influence in this case. As I hope some time later 

 to have an occasion to continue these experiments with the lemon sole 

 under more favourable circumstances, I shall not now give a detailed 

 account of the observations made regarding the food and general develop- 

 ment during the relatively short period of the post-larval stage in which- 

 the larvse lived. 



* After this the lemon gole does not take additional nourishment at such an early stage 

 as the plaice. 



