MUSEUM OF COMPARATIVE ZOOLOGY. 325 



volume of the Annals of Natural History.* In this communication the 

 author gives a brief description and rude figures of four larval stages of 

 the ditch prawn, Palcemon variabilis [Palcemonetes varians Heller T\. 

 The earliest form represented is that which the larva assumes immedi- 

 ately after exclusion from the egg. The first pair of antennae are por- 

 trayed with two terminal, one-segmented branches, a condition not seen 

 in any other figures of the first larval stage of Palcemon. As in Thomp- 

 son's figure of the same stage, only two pairs of swimming-feet are rep- 

 resented. Behind them are the rudiments of the true legs in the shape 

 of three pairs of small, simple, two-jointed processes. The number of 

 abdominal segments is plainly exaggerated. 



In the second stage, "ascertained by observing the moult of the former," 

 the carapace is armed with a dorsal spine at the base of the rostrum, and 

 all the thoracic legs are present ! The posterior pair are destitute of the 

 natatory branches ; the chelse are developed. It is noteworthy that the 

 author expressly states that the abdominal appendages have begun to 

 appear, excepting the last pair. If this be correct, it is certainly an excep- 

 tional order of development among the Macroura. Commonly in this group 

 the posterior pair appear before the other abdominal appendages. 



In the third stage, " also ascertained by witnessing the moult," the 

 carapace has two dorsal and supra-orbital spines, and the posterior pair 

 of abdominal limbs have appeared. 



The fourth stage was not obtained directly from the third by observ- 

 ing the moult. The larva now has three dorsal spines, and, excepting 

 the want of external branches to the last pair of thoracic legs, agrees 

 well with Thompson's third stage. The next moult brought it to the 

 condition of the adult prawn. 



It is obvious from the above account that the number of forms passed 

 through by the larva before reaching the adult shape is much smaller 

 than in the case of Palcemonetes vulgaris, unless there is error in the 

 observations of DuCane. 



The next observation bearing upon the development of Palcemon is 

 found in Fritz Midler's " Fur Darwin." t It consists of a brief description, 

 accompanied by a wood-cut, of what seems to be the first larval stage. 



The researches of Bobretzky upon the development of Palcemon, pub- 

 lished in the Russian language, at Kief, in 1873, J have already been 



* Letter from Captain DuCane, E. N., . . . on the subject of the Metamor- 

 phosis of Crustacea, Ann. Nat. Hist, Vol. II. pp. 178-181, PI. VI, VII. 1839. 



t Fur Darwin. 1864. English Trans, by W. S. Dallas, p. 55, Fig. 27. 1869. 



t Zapiski Kiefs. Obshtshest. Yestestvoispitatalyei, Vol. III. pp. 186-252, PI. IV- 

 VI. 1873. Hofmann und Schwalbe's " Jahresberichte," Vol. II. pp. 317,318. 1875. 



