No. 408.] REVIEWS OF RECENT LITERATURE. 981 
This development of fertilized, enucleated pieces of eggs the 
author calls merogenetic development. 
In cleaving, such fragments tend to be abnormal at first, but by 
progressive self-regulation normal larve are formed. 
In the sea-urchin three larva were got from one egg, and in 
another case an active blastula was obtained from a piece of egg 
one-thirty-seventh of the bulk of the normal egg. 
In this well-controlled Gallic method of cutting a single egg while 
under observation under the microscope we seem much more sure of 
the results than in the former gross Teutonic method of shaking eggs 
wholesale in a tube, to break them to pieces. Still, the author finds 
it necessary to give reasons for rejecting the ideas, — that the egg 
was fertilized before cutting; that the cutting itself acted as a stimu- 
lus; and that the nucleus might have been cut to supply parts to 
each piece of egg. 
In this he seems successful, except as to the last point, and we 
may still have doubts regarding the assumed restriction of the 
nucleus, or the nuclear matter, to one of the pieces. Another possi- 
bility, or indeed probability, the occurrence of polyspermy in these 
fragments, seems to have escaped the author's attention. This may 
vitiate some of his most important conclusions. 
Incidentally the author points out that the cut halves of an egg 
may be drawn together again by the viscous envelope (we presume 
Hammar’s layer) that is not necessarily severed. There is no 
evidence of *cytotropism" in this. On the other hand, there is 
often an abnormal tendency of the blastomeres to fall apart; we 
infer this is a state similar to that induced by Herbst in removing 
calcium. 
It is interesting to find that the enucleated pieces may be bastard- 
ized by sperm of a related animal, but they do not develop when 
treated with the sperm of a widely different animal. In this the 
author sees the importance of the cytoplasm; and he also finds 
evidence of a maturation of the cytoplasm. Thus a ripe and an 
unripe egg in two drops on the same slide, when cut and treated with 
sperm, yielded for the ripe egg cleaving pieces in six out of ten 
cases, and none at all in the unripe eggs. 
Granting that these merogenic larvz are actually fertilized, enu- 
cleated pieces of an egg, it is a very remarkable fact that they have 
eighteen chromosomes in the nuclei of their cells, for this is the 
normal number that is commonly held to have come about by the 
addition of nine chromosomes in the sperm to nine in the nucleus of 
