Jt 
MUSEUM OF COMPARATIVE ZOOLOGY. 30 
In June, July, and the early part, of August, the females of Palæ- 
monetes vulgaris may be found carrying their eggs (which will afford 
different phases of development in different individuals simultaneously) 
fixed to the hairs on the peduncle * of the abdominal appendages, from 
the first to the fourth pair inclusive. Here they receive not only the 
protection of the parent, but also a constant aération by means of the 
gentle backward and forward movement of the abdominal appendages. 
This aération of the eggs seems to be essential to their development, 
for if detached from the mother they invariably die, unless the en- 
closed embryo has very nearly reached the point of hatching. 
All the eggs are not attached directly to the appendages of the abdo- 
men, as in Astacus, but many of them are joined to one another by 
delicate threads drawn out from the secretion which invests each egg. 
Thus large clusters are formed, in which comparatively few eggs are 
fixed immediately to the abdominal appendages. These clusters, again, 
are different from the botryoidal clusters so common among the Brachy- 
ura, in which the eggs are only indirectly connected with each other 
through the mediation of a common stalk from which the eggs depend 
by short pedicels. 
Soon after the escape of the young the parent prawn casts her integ- 
ument, thus ridding herself of the egg-shells which are indissolubly 
fastened to her legs. I have found this moult to take place almost 
invariably within a few hours after the hatching of the eggs.t Com- 
monly this happens in the night, morning discovering the newly-hatched 
brood of zoüw collected at the surface of the aquarium, on the side 
toward the light, and the discarded integument of the parent prawn 
sunk to the bottom. I have never seen the prawn practise that econ- 
omy observed in certain insect larva, which devour their cast-off 
skin. 
The newly-laid eggs are elliptical, about .5 mm. in long diameter. 
tive, is an interesting question for our Western zodlogists to answer. Tho young of 
the fresh-water Caridina Desmarestii, as we know from the observations of Joly 
(Études sur les Movurs, le Développement et des Métamorphoses d'une petite Sali- 
eoque d'Eau Douce (Caridina Desmarestii). Aun. Sci. Nat., 2d series, Vol. XIX. 
1843), are hatched as zoëæ, and undergo a subsequent metamorphosis before attaining 
the adult form. 
* Not to the inner branches, as is stated to be the case with Palæmon serratus, by 
J. V. Thompson (Memoir on the Metamorphoses in the Macroura or Long-tailed 
Crustacea, exemplified in the Prawn (Palamon serratus). Edinburgh New Philo- 
sophical Jour., Vol. XXI. p. 223. 1836). 
+ Joly observed the same thing in Caridina Desmarestii (op. cit., p. 55). 
