$ 294. 
THE CRUSTACEA. 
863 
The young of the Paguridae and Macrura differ more or less from the adult 
animals, © 
But this difference is less with the Poecilopoda, Laemodipoda, 
Stomapoda, Isopoda, and Amphipoda.™ Finally, with the Myriapoda, the 
metamorphosis is limited to the increase of the number of the segments of 
the body, and of the feet.” 
names Megalops, Monolepis and Zoea (Milne 
Edwards, Hist. d. Crust. II. p. 260, 431), until 
Thompson perceived their true nature ; see his 
Zool. Research. &c. Pl. I. and his Memoir on the 
double Metamorphosis in the Decapodous Crusta- 
cea, in the Philos. Trans. 1835, pt. II. p. 539; see 
also the Edinb. New Philos. Jour. No. 20, p. 221, 
and the Entomol. Magaz. No. 14, p. 370. Although 
these observations have been confirmed from dif- 
ferent sides, yet they did not, at first, receive full 
assent, especially on account of the authority of 
Rathké (Miller’s Arch. 1836, p. 187), who opposed 
them. Templeton (Trans. of the Entomol. Soc. 
II. p.115, Pl. XII.) and Westwood (Philos. Trans. 
1835, pt. II. p. 311, Pl. IV.) refuse to give up the 
genus Zoéa; but since Du Cane (Ann. of Nat. 
Hist. III. 1839, p. 438, Pl. XI. or Froriep’s neue 
Notiz. XIII. p. 5, fig. 10-13), has verified, with 
Cancer maenas, the observations of Thompson, 
and Rathké himself (Wiegmann’s Arch. 1840, I. 
p. 246, and Neuest. Danzig. Schrift. loc. cit. p. 39, 
Taf. IV.) has seen the embryos of Hyas under the 
form of a Zoéa, this wonderful metamorphosis of 
the Brachyur& can no longer be doubted. See 
also Steenstrup, in the Oversigt over det kgl. 
danske Videnskabernes Selskabs Forhandlinger, 
1840, p. 15, or Mil/er’s Arch. 1841, p. 218 (Hyas), 
and Goodsir, Edinb. New Philos. Jour. No. 65, 
1842, p. 181, Pl. IIT. fig. 16-18 (Cancer maenas). 
5 The embryos of Pagurus which have a frontal 
spine, were also, before the discovery of Thomp- 
son, taken for species of Zoga; see Philippi, in 
Wiegmann’s Arch. 1840, I. p. 184, Taf. ITI. fig. 
1, 83 also Rathké, Ibid. p. 242, and, Danzig. 
Schrift. loc. cit. p. 29, Taf. ILI. ; Steenstrup, loc. 
cit. ; and Goodsir, loc. cit, No. 65, p. 182, Pl. III. 
fig. 12-14. The difference in form between the 
embryos and the adults is less marked with Asta- 
cus, Homarus and other Macrura; see Rathké, 
Entwick. d. Flusskr.) and in the Danzig. Schrift. loc. 
cit. p. 23, Taf. II. (Homarus) s Du Cane, Ann. of 
Nat. Hist. I. 1839, p. 178, Pl. VI. VII. or Fro- 
riep’s neue Notiz. XIII. p. 3, fig. 4-9 (Palae- 
mon and Crangon) ; Kréyer, Monogr. loc. cit. p. 
37, Pl. VIL GHippolyte and Homarus) ; Joly, Ann. 
d. Sc. Nat. XIX. loc. cit. Pl. IV. (Caridina), and 
Erdi, loc. cit. p. 18, Taf. III. IV. (Homarus). 
6 According to Milne Edwards (Instit. 1838, 
No. 258, p. 397), a cephalothorox and abd may 
already be distinguished with the hatching embry- 
os of Limulus. But the abdomen has only three 
pairs of appendages and its long spine is wholly 
wanting. ‘This naturalist, also, has figured an 
embryo of Cyamus which closely resembles the 
adult (aan d. Sc. Nat. ILI. 1835, p. 328, Pl. XIV. 
ig. 14). 
For the embryos of the Isopoda and Amphipoda, 
see Rathké, Abhandl. loc. cit.; Ann. d. Sc. Nat. 
IL. 1834, p. 139, Pl. XI. ; Zur Morphol. &c. 41, 
Taf. Il. ILI. (Bopyrus, Idothea, Janira, Lygia 
and Amphithée) ; Nov. Act. Nat. Cur. XX. p. 49, 
Tab. I. (Phryxus) ; also Milne Edwards, Ann. d. 
Se. Nat. ITI. 1835, p. 323, Pl. XIV. (Cymothoa, 
Anilocra, Phronima and Amphithoé); finally 
Rathké, in Wiegmann’s Arch. 1839, loc. cit. Taf. 
VI. (Mysis). 
7 See Gervais, Ann. d. 1. Soc. Entomol. de 
France, 1837, and Institut. 1839, p. 22; Waga, Rev. 
Zool. 1839, No. 3. p. 76, or Wiegmann’s Arch. 
1840, II. p. 351; and especially Newport, Philos. 
Transact. 1842, part II. p. 99, and Cyclop. loc. cit. 
III. p. 353, fig. 317-326, also in Froriep’s’ neue 
Notiz. XXI. p. 161. 
