106 



BLASTOGENIC VAEIATIONS. 



that time the arms of the larvae or plutei have attained 

 their maximum length, whilst the body has practically 

 ceased growing. The larvae were then killed by adding 

 corrosive sublimate. They were collected and pre- 

 served in 80 per cent, alcohol, and were subsequently 

 mounted in glycerine and measured under the micro- 



FIGS. 17 AND 18. Larvae of Strongylocentrotus limdus. 



scope by means of a micrometer eyepiece. The body- 

 length, AB, was always measured in 50 different larvae, 

 and a mean taken. In many cases also the anal arm- 

 length, AC, and sometimes also the oral arm-length, AD 

 were measured as well, and these measurements calcu- 

 lated as percentages on the body length. 



In order to determine the effect of staleness of the 

 sex-cells on the size of the larvae, five series of measure- 

 ments had to be made, viz., (1) of the normal larvae ob- 

 tained from the fresh ova fertilised with the fresh 



