No. 406.] REVIEWS OF RECENT LITERATURE. 823 
The work consists of two parts, of which the first treats of the 
teleological laws of nature, and the second of the methods for the 
investigation of these laws. 
Necessary connections or natural laws the author finds to be the 
objects of science. Empirical science, and especially the scientific 
concept of cause, is discussed to some extent, but by far the greater 
part of the book is devoted to what might be termed the philosophy 
of biology. 
Causality, having been defined in terms of general empirical sci- 
ence, and also of special biological science, the biological concepts 
of living, organic, etc., are analyzed in an interesting fashion. 
Under methods of investigation the possibility of methodical work 
in the teleological sphere is discussed in connection with the standard 
methods: induction and deduction. R. M. Y. 
ZOOLOGY. 
The Effect of the Staleness of the Sex-Cells upon Develop- 
ment and upon the formation of hybrids has been reinvestigated by 
Dr. H. M. Vernon. He finds in the case of the echinoderms that 
the number of normal blastula formed from sex-cells kept for some 
time in sea water diminishes about one per cent per hour up to the 
twenty-seventh hour, after which time abnormalities rapidly increase 
in number. Within this period the same decrease was noted whether 
either or both of the sexual products were stale, but after the twenty- 
seventh hour the decrease in normal embryos was most rapid when 
both of the sex-cells were in this condition. The larva: obtained 
from stale sex-cells were of the normal size, though when the sperm 
alone was stale they were often larger, and when the ovum was stale 
they were smaller, than those derived from fresh products. Con- 
trary to the conclusion of the Hertwigs, staleness of the ova in 
hybrids of Sphzrechinus 9 X Strongylocentrotus ó did not increase 
the number of hybrid plutei, though in the reciprocal cross a larger 
percentage of blastulee was produced. The hybrid larve obtained on 
crossing Sphzerechinus ova with Strongylocentrotus spermatozoa vary 
! Vernon, H. M. The Effect of Staleness of the Agata Cells on the Develop- 
ment of Echinoids, Proc. Roy. Soc., vol. Ixv (1899), PP- 3 0-360. 
Vernon, H. M. Cross Fertilization among Suan ak f. Entwickelungs- 
mechanik der Organismen, Bd. ix (1900), pp. 464-478. 
