BLASTOGENIC VARIATIONS. 105 



character of the germ-plasm in a developing animal 

 after fertilisation, it may also have some influence if it 

 be brought to bear on the parental germ-plasms before 

 fertilisation. It seems likely, in fact, that a highly 

 nourished ovum, as compared with one less favourably 

 conditioned, will tend rather to a female than a male 

 development. 



Evidence bearing more directly on the question at 

 issue has recently been obtained by the author, in a 

 research on the effect of staleness of the sex-cells on 

 development.* The method of experiment was to keep 

 the ova or spermatozoa, or both, of the sea-urchin 

 Strongylocentrotus lividus for varying numbers of 

 hours in sea water before permitting fertilisation, and 

 after eight days' development to measure the length of 

 the larvae and see if they differed in size from normal 

 larvae. As other observations on larvae obtained from 

 these artificial fertilisations will be referred to later, 

 the experimental procedure adopted may be briefly in- 

 dicated. It consisted in shaking pieces of the ovaries 

 and testes of several ripe specimens of the Echinoid 

 in small jars of water, and mixing portions of their con- 

 tents either immediately, or after a given number of 

 hours. The mixed solutions were allowed to stand for 

 an hour, and were then poured into large jars holding 

 from 2 to 4 litres of sea-water. These were placed in 

 a tank of running water, whereby the temperature was 

 kept nearly constant, it varying less than a degree dur- 

 ing twenty-four hours and not more than two degrees 

 during the whole course of the experiment. The fer- 

 tilised ova were allowed to develop for eight days, as by 

 *Proc. Roy. Soc., vol. Ixv. p. 350, 1899. 



