176 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
two cells. As the phenomena of copulation are not the same in all the 
genera, it is necessary to deal with each set of observations separately ; 
Moina rectirostris and M. paradoxa ; Daphnia pulex and D. longispina ; 
Sida crysfallina ; Bythotrephes longimanus ; Polyphemus oculus ; and 
Leptodora hyalina are treated of in succession. 
Two series of phenomena are dealt with in this memoir, and though 
both are concerned with the winter-egg of the Daphnida, they have no 
direct connection with one another. One has to do with the history 
of the conversion of the germinal vesicle into the egg-nucleus, and the 
other with the origin and fate of the copulation-cell. 
The conversion of the germinal vesicle, and the formation of the 
polar globules is effected in essentially the same way as in other eggs 
which require fertilization. This fact is more important than its 
determination in other groups since Daphnids are capable of partheno- 
genetic as well as of sexual reproduction. The law of numbers of the 
polar globules is confirmed. Dealing with the exceptional cases lately 
described by Platner and by Blochmann, the authors point out that, in 
both cases, the eggs are arranged for sexual development ; they are 
capable of fertilization, to effect which their germ-plasm must be halved, 
or, in other words, a second polar globule must be formed. 
With regard to paracopulation the facts are, shortly, these. In the 
winter egg (or egg requiring fertilization) of six species of Daphnida, 
belonging to four genera, a cell is formed in the egg-cell during the 
ovarial development of the egg. In the still young and yolkless egg of 
Moina a part of the nuclear substance actively passes out from the 
germinal vesicle into the surrounding mass of protoplasm, organizes 
itself into a real nucleus (paranucleus), and at the same time surrounds 
itself with a cell-body. 
When the egg is laid the copulation-cell is quite passive. After 
fertilization by a sperm-cell, the process of cleavage begins and goes on 
through a varying number of stages ; the copulation-cell moves towards 
one of the cleavage-cells, which are sunk in the interior of the yolk, sends 
out short processes, and fuses with it ; first the cell-bodies and then 
the nuclei unite. 
Though the authors discuss at some length the significance of these 
phenomena they are at present unable to give an explanation of them. 
It may, however, be supposed that we have here to do with a very 
general process. At any rate it would be very strange if it occurred only 
in Daphnids. 
New Entoniscan parasitic on the Pinnotheres of Modiola.* — 
MM. A. Giard and J. Bonnier describe Pinnotherion vermiforme g. 
et sp. n., a parasitic crustacean which lives on a crab (Pinnotheres') which 
is itself parasitic on a Mollusc (Modiola). It was detected in the form 
of a violet-grey mass, which resembles an egg-mass of Grapsion Cavolinii ; 
this was the incubatory cavity of the female. The generic and specific 
characters are described. Only two males, and those degraded, were 
found ; they resemble the males of Grapsion and Portunion, but are 
almost entirely destitute of pigment ; the spermatozoa present the 
* Comptes Reuflus, cix. (1889) pp. 914-6; Ann. and Mag. Nat. Hist., v, (1890) 
p. 124. 
