ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 65 



50 per cent, of sea-water suffices to bring about the same result as the 

 entrance of a spermatozoon. The eggs were left in the solution for about 

 two hours, and tben returned to normal sea-water. They segmented, 

 formed blastulae, gastrulse, and plutei, normal in every" respect, except 

 that fewer eggs developed, and that the development was slower than 

 the normal. With each experiment a series of control experiments was 

 made to guard against the possible presence of spermatozoa in tbe sea- 

 water. 



The unfertilised egg of the sea-urchin contains all the essential ele- 

 ments for the production of a perfect pluteus. All the spermatozoon 

 needs to carry into the egg for the process of fertilisation are ions to 

 supplement the lack of favourable ions in the water, or to counteract the 

 effects of the other class of ions, or both. " The spermatozoon may, 

 however, carry in addition a number of enzymes or other material. The 

 ions and not the nucleins in the spermatozoon are essential to the pro- 

 cess of fertilisation." He suggests that in mammals the ions in the 

 blood prevent parthenogenesis, and that a transitory change in these 

 might allow of it. At present it seems hardly safe to say more than 

 that these are very remarkable experiments. 



Staleness of Sexual Cells and its Influence on Development.* — 

 Dr. H. M. Vernon notes that the effect of varying degrees of staleness 

 of the ova and sperms of an organism upon subsequeut development 

 appears to have been little studied, though such a condition must be a 

 factor of frequent occurrence under natural conditions. He tinds : — ( 1) If 

 the ova and sperms of the Echinoid Strongylocentrotus lividus be kept for 

 various times in sea-water before fertilisation, then, fur about the first 

 twenty to twenty-seven hours, the number of normal blastulae formed 

 diminishes only about 1 per cent, per hour. After this, abnormal de- 

 velopment sets in rapidly, so that generally, after a further nine hours or 

 so, no blastulae at all are obtained. The rate of falling off in the num- 

 ber of normal blastulae may increase to as much as 18*9 per cent, per 

 hour. (2) If ova not more than twenty-seven hours stale be fertilised 

 with equally stale sperm, practically as many blastulae are obtained as 

 ■when stale ova are fertilised by fresh sperm, or fresh ova by stale sperm. 

 After twenty-seven hours, however, the number of blastulae obtained 

 with both products stale falls off more rapidly. (3) Larvae obtained 

 from stale ova and stale sperm are practically normal in size ; those 

 from fresh ova and stale sperm are distinctly larger than the normal ; 

 those from stale ova and fresh sperm are distinctly smaller. 



Analysis of the Genus Micraster.f —Dr. A. W. Howe has done a 

 fine piece of work in this analysis of the genus Micraster, as determined 

 by rigid zonal collecting from the zone of Bhynchonella cuvieri (low- 

 zonal) to that of Micraster cor-anguinum (high-zonal) in the Chalk. 

 Two thousand examples have been measured and analysed, and no speci- 

 men has been included in the summary unless its zonal position was 

 accurately determined. Six hundred photomicrographic negatives of the 

 special features of the test were made, in order that mere conjecture 

 might play no part in the inquiry, and that these important aids to 



* Proc. Roy. Soc, lxv. (1S99) pp. 350-60. 

 t Quart. Journ. Geol. Soc, lv. (1899; pp. 494-547 (5 pis ). 

 Feb. 21st, 1900 F 



