144 HIROSHI OHSHIMA 



decided conclusion from such few cases and numbers one 

 can hardly see any effect of the synthetic sea-water on the 

 production of doubles or reversed if allowed to act earlier in 

 one culture than in others. 



One might reasonably expect that the artificial treatment of 

 tlui egg and sperm might have caused some disturbance from 

 the normal development of the larva. This is of course quite 

 possible, but I may only mention that it is curious to see that 

 among such material as the sea-urchin egg so connnonly used 

 for study and demonstration in embryological work only 

 a very few cases of the abnormalities in question have been 

 noticed. 



One of the most important factors which differ more or less 

 from the conditions in nature is the food supply. The method 

 of feeding marine larvae on diatom cultures, through which 

 many different forms of pelagic larvae have been successfully 

 reared, is relatively a recent introduction. The result is very 

 often over-feeding. In an over-fed larva hypertrophy and 

 other disturbances in growth is quite conceivable. From 

 uneven distribution of food in the culture jar and fi'om a 

 different state in the health of larvae, over-fed and under-fed 

 individuals may arise within one and the same jar. The 

 obliteration of the normally-formed left dorsal pore, w^hich 

 seems to me a direct cause of the production of the double 

 hydrocoele and situs inversus of the Echinus larvae, may 

 be associated with the excess of diatoms and other minute 

 organisms in the jar. Whether it is physiological or mechanical 

 it is hard to decide at present. 



Eunnstrom (25, pp. 321-2) found that the larvae of 

 Strongylocentrotus showed the degeneration of organs 

 when over-fed on yolk. The echinus-rudiment was above all 

 the most sensitive to the treatment and degenerated com- 

 pletely. Undigested yolk granules were found migrating 

 everywhere, even scleroblasts were laden with them and the 

 absorption of calcareous bodies followed. The effect of over- 

 feeding on diatoms will naturally be very different from this. 

 Though somewhat difficult to control (MacBride, 15 



