20 Crust . 
CRUSTACEA. 
ILecker observes four stages in the egg of Cyclops immediately pre- 
vious to fertilization : — (a.) There is a single large macronucleus or two 
smaller macronuclei, much vacuolated. Near by there are two small 
faintly coloured micronuclei. There are eight pairs of parallel threads 
scattered throughout the egg. (b.) The nuclear-membrane has dis- 
appeared. The macronucleus is diminished in size, but the micronuclei 
are still present. The threads have arranged themselves in four pairs at 
either pole, (c.) Eight rod-like chromosomes, apparently derived from 
the threads observed in a. and b., are seen in the membraneless nucleus. 
Near the nucleus an isolated mass of protoplasm appears, (d.) A distinct 
spiudle-shaped figure is formed, four of the chromosomes moving off 
towards either pole. 
Solger has observed the formation of both polar bodies in the case of 
numerous eggs of Balanus improvisus. The phenomena are similar to 
those described by Nussbaum as occurring in the case of Pollicipes. 
Leichmann opposes Rosenstadt’s view that the oviposition of Asellina 
exactly resembles that of Ouiscus. The genital orifices do not disappear 
at the ecdysis which follows fertilization, but are hidden by brood- 
lamellae. Fertilization takes place in the ovary, the middle part of the 
oviduct previously swelling to form a receptaculum seminis. 
Parker (1) deals with the minute structure and development of the 
eye of the lobster. With regard to the general type of structure, he dis- 
agrees with the views of Patten, Reichenbach, and Kingsley, and con- 
siders that the retina is formed from a thickened portion of the hypoder- 
mis which undergoes no involution. Whatever involution takes place 
probably concerns the optic ganglion alone. 
Lebedinski describes the development of the crab Eriphya spinifrons 
as far as the zocea stage. A thick germinal disc appears, which gives rise 
to all three layers. Two new independent thickenings in front of the 
disc form the cephalic lobes and give rise to the brain, eyes, etc. The 
subsequent changes in the disc and the cephalic lobes are dealt with in 
detail. The first appearance and later structure of the heart are described. 
The rudiments of segmental organs appear shortly before the zooea stage, 
and resemble homologous structure in Annelids and Mollusca. 
Herrick has investigated the development of Homcirus , and finds it 
to resemble strongly that of Alpheus, except in the earlier stages. The 
pyramid structure of the yolk is not observable. Protoplasm migrates 
from the centre to the periphery. Gastrulation commences with a small 
patch of cells at one side of the egg, which contains a circular depression 
— the blastopore. The naupliar appendages appear nearly simultaneously. 
The endoblast is established at a late stage, when eight or ten pairs of 
appendages are visible. 
Canu (l) finds, in opposition to the views of Claus and Della Yalle, 
that the Copepod genus Enlerocola is without mandibles. These append- 
ages are lost during the passage from the last nauplian to the first cvclo- 
poid stage. In the female, the second cyclopoid stage is that at which the 
parasite seeks its host, thereafter to become stationary. This is not the 
