1895.] on the Development of Echinoderm Larvce. 383 



was found that if the ova were placed in water at about 8 or 25 0. 

 for an hour, or even for a minute, at the time of impregnation, the 

 resulting larvae after eight days development were, on an average, 

 4*6 per cent, smaller than those impregnated at from 17 to 22, 

 though all the subsequent conditions of development were identical. 

 If kept at the abnormal temperature for only ten seconds during 

 impregnation, the resulting larvae were only 1*7 per cent, smaller, 

 probably because the time was too short for all the ova to become 

 impregnated under the abnormal conditions. Differences of tempera- 

 ture during the course of development have in comparison a much 

 slighter influence. Thus larvae allowed to develop in water at 17 

 to 22 are only about 2 per cent, larger than those allowed to develop 

 at 15-7 to 17, or at 22 to 237. 



The time of the year when the artificial fertilisations are prepared 

 has a very marked influence on the size of the larvae. Thus, those 

 obtained in the middle of August are about 20 per cent, smaller than 

 those obtained in April, May, and October, whilst those obtained in 

 June and July are intermediate in size. This is probably due to 

 the comparative immaturity of the ova and spermatozoa in the off- 

 breeding season. 



The salinity of the water has a great influence on the development. 

 Larvae allowed to develop in water containing 50 c.c. of distilled 

 water per litre are 15'6 per cent, larger than those grown under 

 normal conditions, and those in water containing 25 c.c. per litre 

 9'5 per cent, larger. On the other hand, in water containing 150 c.c. 

 of distilled water per litre they are 4'3 per cent, smaller. In water 

 more concentrated than the. normal they remain practically un- 

 changed, but larval grown under normal conditions from ova 

 impregnated in concentrated water are 1*6 per cent, larger. 



It was thought to be of interest to determine the effects which the 

 various colours of the spectrum have upon development, though these 

 are not conditions of environment which occur in nature. Larvae 

 allowed to develop in the blue light of copper sulphate solution are 

 4'5 per cent, smaller than the normal, and those in the violet-blue 

 light of Lyons blue solution 7'4 per cent, smaller. Those grown in 

 the green light of nickel nitrate solution are 4'8 per cent, smaller, 

 and those in red and yellow lights respectively 6'9 per cent, and 

 8*9 per cent, smaller. The development of the larvae seems to be but 

 little affected if it is carried out in absolute darkness, the size only 

 being diminished by 1*3 per cent. Larvae grown in semi-darkness 

 are apparently 2'5 per cent, larger than the normal. 



The body-length of the larvas appears to be uninfluenced by the 

 number of larvae developing together in a given volume of water, if 

 it be kept below 30,000 per litre. The arm-lengths are, on the other 

 hand, considerably affected. The aboral and oral arm-lengths of 



