80 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE, 
up with a jelly-like substance, and in which stellate con- 
nective tissue-cells often develop. At the same time Metsch- 
nikoff holds the Echinoderms and the Ceelenterates to be 
two distinct types, which must, however, be placed near one 
another in classification. He finds the same degree of simi- 
larity between them as between the higher worms (Hirudines, 
Gephyrea, and Annelids) and the Arthropods. 
Edouard Van Beneden, under the title ‘ De la distinction 
originelle du Testicule et de l)Ovaire” (Brussels, 1874), has 
published an exceedingly important account of the develop- 
ment of the sexual products in Hydractinia echinata, accom- 
panied by some general considerations of philosophic import. 
After reviewing recent writings, in which the inference has 
been drawn that throughout the animal kingdom ectoderm 
and endoderm are homologous (homogenous) structures, Van 
Beneden proceeds to point out the discrepancy in the various 
accounts of the origin of the sexual products in the Ceelen- 
terata, those organisms which, as he justly observes, most 
readily lend themselves to the investigation of the question, 
from which of these two layers are the ova and the sperma- 
tozoa respectively developed. One source of discrepancy is 
no doubt this—that few observers have made use of the 
system of cutting sections, or, on the other hand, have 
employed species for observation which are sufficiently trans- 
parent to allow of a perfectly satisfactory examination of the 
problem. Furthermore, there is this undoubted fact, which 
is well recognised in the case of the generative and 
other organs throughout the animal series, namely, that an 
organ travels very frequently in the course of its development 
to a considerable distance from its seat of origin, and comes 
to occupy a totally different relation to surrounding parts 
from that which it primitively occupied. Hence, unless an 
observer detects the actual very first commencement of ovary 
or testicle, he may be led to assign to them as a seat of origin 
some intermediate position occupied by them secondarily, or 
in transitu. Van Beneden finds in Hydractinia that there isa 
very interesting mode of development for the testicle, similar, 
we may record, to what Kleinenberg, of the Zoological Sta- 
tion, Naples, has recently observed by careful sections in the 
case of Tubularia indivisa. The testicle and spermatozoa 
develop at the expense of the ectoderm, and result from the 
progressive transformation of a cellular fold formed primi- 
tively by invagination. 'The eggs, on the other hand, are 
developed exclusively at the expense of the epithelial cells 
of the endoderm. ‘They remain, up to their maturity, sur- 
rounded by the elements of the endoderm. Moreover (and 
