MUSEUM OF COMPARATIVE ZOOLOGY. 305 



In June, July, and the early part of August, the females of Palce- 

 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 aeration by means of the 

 gentle backward and forward movement of the abdominal appendages. 

 This aeration 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 Astactos, 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 zoese 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 larvte, 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 zoologists to answer. The young of 

 the fresh-water Caridina Desmarestii, as we know from the observations of Joly 

 (Etudes sur les Mceurs, le DeVeloppement et des Metamorphoses d'une petite Sali- 

 coque d'Eau Douce (Caridina Desmarestii). Ann. Sci. Nat., 2d series, Vol. XIX. 

 1843), are hatched as zoese, and undergo a subsequent metamorphosis before attaining 

 the adult form. 



* Not to the inner branches, as is stated to be the case with Palcemon serratus, by 

 J. V. Thompson (Memoir on the Metamorphoses in the Macrource or Long-tailed 

 Crustacea, exemplified in the Prawn (Palcemon serratus). Edinburgh New Philo- 

 sophical Jour., Vol. XXI. p. 223. 1836). 



t Joly observed the same thing in Caridina Desmarestii (op. cit., p. 55). 



