182 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



being the more alkaline — that is, having less carbon dioxide — 

 which is due, according to Professor Benjamin Moore, to the 

 greater amount of photosynthesis in progress, caused by the 

 relatively greater quantity of green algae growing on the walls 

 of the pond.* Whether this reduced amount of carbon dioxide 

 would have any effect either in increasing or retarding the 

 spawning and subsequent development of the fish has not 

 yet been determined. 



In looking now at the records of the hatchery for the 

 seventeen successive years (1904 to 1920, inclusive) we find 

 that the dates for the first observed fertilised eggs range from 

 the middle of January, 1920, to March 3rd, 1904). Excluding 

 these two records as exceptional, we have a run of 15 con- 

 secutive years with dates ranging from February 5th to 26th, 

 and the average date for the first fertilised plaice eggs in the 

 Port Erin pond is about February 20th. The average tempera- 

 ture of the pond at that time is 40° F. 



The dates of the first hatching of larvae in these years 

 ranges from February 9th, 1920, to March 30th, 1904, and the 

 average date is about March 13th, when the average temperature 

 of the water is 41° F. The dates when the first larvae are 

 set free in the sea have varied from February 23rd (1914 and 

 1920) to April 10th (1904), and the usual date is about March 

 20th, when the sea- water temperature averages 44° F. 



Turning now to our records of the phyto-plankton in the 

 sea, we find that the earliest date in the 13 years (1907-1919) 

 is February 5th (1907) and the latest April 13th (1908). 

 Omitting February and April, we have a run of ten consecutive 

 years (1910 to 1919) when the dates range from March 4th to 

 22nd, and a central date for the beginning of the Diatom 

 increase in spring may be taken as about the middle of March. 

 The actual phyto-plankton maximum ranges in these years 



* Moore finds that a shore pool at Port Erin full of growing green weed 

 is distinctly more alkaline than the water of the bay, in April. 



