REPORT ON THE SPAWNING OF THE COMMON SOLE. 7 



As to the latter, a very healthy batch of eggs, spawned on April 28th, 

 hatched out in numbers on the seventh day, while eggs spawned about 

 a week later, and from thence onwards, hatched out on the fifth day, 

 when the temperature of the water was between 13° and 14° C. in 

 the daytime. Both these times are considerably quicker . than that 

 of eggs studied by Cunningham, when the water was colder. 



I found that even the particularly healthy batch of eggs above 

 referred to, in which the mortality all through had been small for 

 teleost eggs, sank to the bottom, as noted by Cunningham, half a day 

 or so before hatching, and less healthy eggs ceased to float a day or two 

 earlier. Tor this reason it seems to me that the plan of keeping the 

 eggs, which I adopted primarily for my own convenience in studying 

 and preserving different stages at slioit intervals, would be more suited 

 to these eggs than the usual narrow-mouthed, wide gauze-bottomed 

 hatching jars. The plan I refer to is that of the plain wide-mouthed 

 glass beaker, with a safety siphon ; the form of the latter used being 

 not the sand filter bottom, but that with a glass funnel covered with 

 gauze, which I found being used in the laboratory. A small jet of 

 water, if directed so as to strike the glass side of the vessel a little 

 above the surface of the water, and at a small angle to both the glass 

 and the horizon (pointing downwards), seemed sufficient to keep the 

 eggs circulating, since the surface water being made to revolve, any 

 egg on the surface must soon come within reach of the water coming 

 down the side of the glass, and is then driven gently downwards. 

 With this adjustment the eggs, having small buoyancy, tend to collect 

 on the gauze entrance to the exit funnel ; but this can, if necessary, 

 be corrected by making a second small jet of water, from a tube 

 carried beneath the surface, gently play across the gauze mouth of 

 the funnel. 



The advantages of this type of vessel over the usual hatching jar 

 to the embryologist are obvious, while to the practical fish hatcher 

 it is a consideration that he can easily keep the glass bottom clean 

 and free from dead eggs by the use of a dipping tube, so that when 

 the eggs sink before hatching, they have not to lie on a bed of putrid 

 eggs. Moreover, the apparatus can be at once moved into any light for 

 inspection, and will work with comparatively little water. 



VI. Preliminary Remarks on certain ]\Ioi;piiological Conclusions 



TO BE DRAWN FROM A StUDY OF THESE EtIGS. 



I have for some tliree or four years been one of those who are 

 impressed with the strength of the case for the " Concrescence Tlicory," 

 and with the lamentable waste of time in futile researches and discus- 



