234 SCIENCE PROGRESS. 



It is one of the chief recommendations for the use of 

 sea-urchin larvse in experiments on variation that artificial 

 fertilisations can be carried out all the year round. In a 

 state of nature probably these organisms only breed for a 

 few months in the winter and early spring-, but at Naples, 

 for these experiments were carried out at the Zoological 

 Station situated there, I was able to obtain larvae through 

 all the summer months. It was interesting to note, how- 

 ever, that larvse obtained in these months were much 

 smaller than those obtained in the spring, those in August 

 being veritable dwarfs, some 20 per cent, or more smaller 

 than those obtained in April, May and October. Those 

 in June and July were intermediate in size. This dwarf- 

 ing of the larvse is presumably due to the comparative 

 immaturity of the ova and spermatozoa in the off-breeding 

 season, for the conditions of development were in other 

 respects practically the same. It suggests a reflection as 

 to the possibility of a somewhat similar condition existing 

 amongst higher animals, Le., as to whether the offspring of 

 animals conceived at the bes'innins: or end of the term of 

 reproductive capacity are any smaller, or less well formed 

 than those arising in the plenitude of functional power. 

 At present there appears to be no evidence that this is the 

 case, though this may be due to its not having been sought 

 for. 



The next condition of environment to be examined was 

 that of the salinity of the sea water. The larvae were found 

 to be exceedingly sensitive to changes in this condition. 

 Thus larvse allowed to develop in water to which one part 

 in twenty of fresh water had been added, were 15*6 per 

 cent, larger than the normal, and in that containing one part 

 in forty of fresh water, 9*5 per cent, larger. The addition 

 of too much fresh water has a harmful effect however, as 

 with one part in seven of fresh water, the larvse were 4*3 

 per cent, smaller. By more concentrated water than the 

 normal the larvse were apparently practically unaffected. 

 This striking reaction to slight changes in the salinity of 

 the sea water must frequently be in operation under natural 

 conditions. Thus in the Challengej'' Expedition it was 



