116 HIROSHI OHSHIMA 



which had been prepared by (tvaporating. A right hydrocoele 

 appeared but the amniotic invagination failed to appear, 

 and the larvae refused to develop further. 



1915 (p. 335). From among the larvae treated as above 

 the most promising ones were isolated and fed on abundant 

 N i t z s c h i a . One larva produced a five-lobed hydrocoele on 

 the right side. 



1916 (p. 335). In both groups, those; kept throughout in 

 ' hypertonic ' sea-water and thost! put back in normal sea- 

 water, after being treated for one to three days, were found 

 some larvae with an unmistakable right hydrocoele provided 

 with five tentacles. 



1917 (pp. 335-7). ' Hypertonic ' sea-water was prepared this 

 time by adding common salt to sea-water. The fourth-day 

 larvae were transferred to ' hypertonic ' sea-water and allowed 

 to remain in it for six days, after which period they were again 

 put back in normal sea- water. The larvae with double hy drocoeles 

 were about 2 per cent, in one jar, while at least 5 per cent, 

 were in the other. Amongst hundreds of controls there was 

 found only one specimen which had a double hydrocoele. 



The result obtained in 1919 was so similar to that of the fore- 

 going year that he thought it unnecessary to publish anything 

 about it. 



Before further discussing the causes and processes of forma- 

 tion of the abnormalities, let us stop for a moment to consider 

 some questions which may naturally arise in the reader's mind. 

 These are the questions of fundamental importance : (1) Is 

 not the writer's discovery due to an error of observation ? 

 (2) Is not the occurrence of such abnormal larvae also common 

 in nature for this particular species — at least in a particular 

 season and at a particular place '? (3) Is not the scantiness 

 of records due to negligence on the part of previous observers ? 

 (4) Is not the so-called ' abnormal ' condition hereditary "? 



(1) It is rather incredibly frequent to find that even careful 

 observers make an error in the use of the so-called endless 

 screw of the fine adjustment of some microscopes so as to 

 confound the upper surface of the object with the under 



