50 REVIEWS. 
‘there is no doubt that, if a solution of the questions arising 
concerning the genealogical relations of different animals among 
themselves is possible, comparative embryology will afford the first 
and truest principles.” He modestly suggests that the facts pre- 
sented in his paper will widen our views on the genetic relations 
of the insects to other animals, and refers to the opinion first ex- 
pressed by Fritz Miller (Fir Darwin, p. 91), and endorsed by- 
Heeckel in his “ Generelle Morphologie,” that we must seek for the 
ancestors of insects and Arachnida in the Zoéa form of Crustacea. 
He cautiously remarks, however, that “the embryos and larva ob- 
served by me in the egg-parasites, open up a new and wide field 
for a whole series of such considerations; but I will suppress 
them, since I am firmly convinced that a theory which I build up 
to-day, can easily be destroyed with some few facts which I learn — 
to-morrow. Since comparative embryology as a science does not 
yet exist, so do I think that all genetic theories are too premature, — 
and without a strong scientific foundation.” 
_ The reviewer is perhaps less cautious, but he cannot refrain from 
making some reflections suggested by the remarkable discoveries 
of Ganin. In the first place, these facts bear strongly on Cope 
and Hyatt’s theory of evolution by “acceleration and retardation.” 
In the history of these early larval stages we see a remarkable ac- 
celeration, or hurrying up, of the embryo. A simple sac of unor- 
ganized cells, with a half-made intestine, so to speak, is hatched, 
and made-to do the duty of an ordinary, quite highly organized ` 
_larva. Even the formation of the “primitive band,” usually the 
first indication of the organization of the germ, is postponed 
to s comparatively late period in larval life. The different ana- 
tomical systems, the heart, with its vessels, the nervous system, 
and the respiratory system (tracheæ), appear at longer or shorter 
intervals, while in one genus, the tracheæ are not developed at all. 
Thus some portions of the animal are accelerated in their develop- - 
ment more than others, while others are retarded, and in others 
still certain organs. are not developed at all. Meanwhile all live 
in.a fluid medium, with much the same habits, and surrounded 
with quite similar physical conditions. 
The highest degree of acceleration is seen in the reproductive 
organs of the Cecidomyian larva of Miastor, which produces & 
summer brood of young, alive, and which live free in the body of 
the child-parent ; and in the pupa of Chironomus, which has. been 
