ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
155 
tlie dominant idio2>lasm of the nucleus in a definite way, as clay in the 
sculptor’s hand. The different appearance and function of ovum and 
spermatozoon and their mutual attraction rest on secondary adaptations, 
qualified to insure that they shall meet and that their idioplasmata shall 
come into contact ; and as with the cells, so the differentiation of persons 
into male and female is also secondary ; the so-called sexual characters 
are nothing but adaptations to insure the union of the hereditary ten- 
dencies of two individuals. 
Boveri has recently shown that Weismann and Strasburger are right 
in considering that the sperm-nucleus can play the part of ovum-nucleus 
and vice versa, for he removed the nucleus from an Echinoid egg by 
agitation, introduced spermatozoa, got a regular segmentation and a 
complete larva which lived for a week. Furthermore, if eggs of Echinus 
microtuherculatus be fertilized with the spermatozoa of Sphserechinus 
granulatus {sic : ? granularis), larvm are developed with the true characters 
of the second species. Although Weismann’s first interpretation of the 
polar body of the metazoan ovum is probably not correct, his idea — that 
the first dominant protoplasm is different to that of a later period — is 
justified by subsequent researches ; the last word has, probably, not yet 
been said on this question. Prof. Vines is probably right in questioning 
whether sexual reproduction is the only factor which maintains Metazoa 
and Metaphyta in a state of variability ; at the same time, no one will 
dispute that it is a most active means of heightening variations and of 
mingling them in favourable proportions. Sexual reproduction has 
arisen by and for natural selection as the sole means by which individual 
variations can be united and combined in every possible proportion. 
As to the inheritance of acquired characters, it is pointed out that 
Boveri’s observations prove that, among animals, the body of the ovum 
contributes nothing to inheritance ; if acquired characters are trans- 
mitted, they must be so by means of the nuclear matter of the germ-cells 
— in fact, by the germ-plasm, and that not in its patent, but in its latent 
condition. 
Divergent Evolution and Darwinian Theory."^ — The Eev. J. T. 
Gulick discusses his theory of divergent evolution under the heads 
of (1) Some degree of local separation under different environments ; 
(2) Darwin’s theory of natural selection through the advantage of the 
divergence of character ; (3) Darwin’s theory that exposure to different 
environments is essential to diversity of natural selection ; (4) divergent 
forms of sexual selection, and (5) Darwin’s reference to the causes 
which check the crossing of varieties. He concludes that, though 
Darwin has not recognized segregation, which is the independent propa- 
gation of different variations, as a necessary condition for the production 
of divergent races and species, he has pointed out one process by which 
segregation is produced in nature ; this is geographical or local separa- 
tion under diflerent environments. This process is an important cause 
of segregation resulting in divergent evolution, but this is not the only 
cause producing segregation and divergence, for in some cases the 
isolated portions of a species, while exposed to the same environment, 
acquires divergent habits in the use of it; in other cases, without 
* Amer. Journal Science, xxxix. (1890) pp. 21-30. 
