356 Dr. H. M. Vernon. The Effect of Staleness of the 



The conclusion we have arrived at is not altogether an expected one, 

 as far as one could form any expectation from indirect evidence. Thus, 

 as before mentioned, 0. and E. Hertwig found that the ova of certain 

 Echinoids, if kept ten to twenty hours, underwent fertilisation in very 

 much larger numbers than freshly shed ova. The fresher and better 

 the condition of the sperm, however, the better the chance of cross 

 fertilisation. Again, in a former paper,* I showed that hybrid larvae 

 from the ova of Stnmgylocentrotus lividus and the sperm of Spluerechinus 

 granulans could only be obtained in any number during the months of 

 July and August, when the sexual products of Strong ylocentrotus were 

 found to reach their minimum maturity. Those of Sphcerechinus were, 

 on the other hand, in a mature condition. One would therefore be 

 inclined to conclude that in the present experiments, stale ova ferti- 

 lised by fresh sperm would yield a larger proportion of blastulae than 

 fresh ova fertilised by stale sperm. It must be remembered, however, 

 that the conditions are essentially different. Thus in direct fertilisa- 

 tion, it is the natural property of every ovum, whether fresh or stale, 

 to undergo fertilisation by any spermatozoon which still preserves its 

 vitality ; whilst in cross fertilisation it is, as a rule, the natural pro- 

 perty of every ovum to resist such impregnation, and this resistance 

 is only overcome when the vitality is diminished by keeping the ovum 

 in water, or by other means. 



We have thus far examined only how far the staleness of the sexual 

 cells affects the number of normally developing blastulae. Does^it 

 have any more permanent effect, and do the larvae developed from 

 stale products differ either in form or size from those developed from 

 fresh products 1 In the paper just mentioned, a few experiments upon 

 this subject were recorded, and these showed a very distinct effect to 

 be produced : but as they were not very numerous, no great stress was 

 laid upon them. They have since been repeated, and sufficient con- 

 firmation of them obtained. The method of experiment was, as usual, 

 to mix portions of the liquids containing the stale or fresh ova and 

 sperm, and then, after an hour, pour them into jars containing about 

 2J litres of sea water. These jars were kept in a tank of running sea 

 water at a practically constant temperature for eight days, and the 

 larvae were then killed by the addition of corrosive sublimate, and pre- 

 served in 80 per cent, alcohol. They were then mounted in glycerin, 

 and measured under the microscope in groups of fifty, by means of a 

 micrometer eye-piece, f In a complete experiment, five series of mea- 

 surements had to be made, viz. : (1) of the normal larvae obtained 

 from the fresh ova fertilised with fresh sperm, (2) those from stale ova 

 . and stale sperm, (3) from stale ova and fresh sperm obtained from 

 another freshly opened Echinoicl, (4) from fresh ova and stale sperm, 

 * ' Phil. Trans ,' B, 1898, p. 465. 



t For fuller details of the method, vide ' Phil. Trans.,' B, 1895, p. 577. 



