324 BULLETIN OF THE 
opment of Astacus, Rathke came to the conclusion that the prawn too 
acquires, while still within the egg, all the external parts (excepting the 
sexual organs) which are found in the adult, and that it is subject to no 
greater structural changes after leaying the egg than a bird is! After 
further researches upon the development of Decapods, Rathke acknowl- 
edged his error, and his handsome tribute to J. V. Thompson, in this 
connection, is a notable example of candor.* 
The changes which the young suffers after leaving the egg were first 
observed by J. V. Thompson. In the summer of 1828 he obtained the 
first stage of the larva by hatching the eggs of Palemon serratus, and in 
à paper published in 1836 t gave a rough figure of this, together with 
two older larval prawns which he supposes to belong to the same species, 
although they were captured free-swimming. 
How much allowance must be made for inaccuracy in Thompson’s 
figures it is hard to say. The first stage is represented with but two 
pairs of cleft members; in the second stage the larva has acquired: an 
additional pair of swimming-feet, the sixth pair of abdominal appendages 
are present, and form with the telson a terminal fin about like that in 
our third larval stage. There is yet no dorsal spine on the carapace, 
and the first pair of antenna are still simple. 
The third stage apparently represents a phase somewhat more ad- 
vanced than our sixth stage. The carapace is now armed with three 
spines on the median dorsal line, and a supra-orbital spine on each side. 
All of the appendages are now present, the chele are well formed, and 
all of the thoracic members, not excepting the posterior pair, are fur- 
nished with a natatory branch. The flagellum of the second pair of 
antenne is in the condition of the adult, being divided into an indefinite 
number of annuli. In other respects the young prawn agrees pretty well 
with the sixth stage of Palamonetes. 
The most complete account of the larval stages of Palcmon up to the 
present time is that of Captain DuCane, published in 1839, in the second 
* Zur Entwickelungsgeschichte der Dekapoden. Arch. f. Naturgesch., 1840, I. 
p. 248. 
Beiträge zur vergleichenden Anatomie und Physiologie, Reisebemerkungen aus 
Skandinavien, p. 46. Neueste Schriften der Naturforsch. Gesell. in Danzig, Vol. III. 
1842. 
t Memoir on the Metamorphosis in the Macroure or Long-tailed Crustacea, exem- 
plified in the Prawn (Palemon serratus), Edinburgh New Philosoph. Jour., Vol. 
XXI. pp. 221—223, Pl. I. 1836. A short notice of this paper appears in the ** Ab- 
stracts of the Papers printed in the Philosophical Trans, of the Royal Soc.,” Vol. 
III. p. 371. 1836. 
