^294. 



THE CRUSTACEA, 



m 



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. PI. 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 

 Rathke (MuUer''s Aych. 1836, p. 18"), who opposed 

 them. Templeton (Trans, of the Entomol. Soc. 

 II. p. 115, PI. XII.) and Westiuood (Philos. Trans. 

 1835, pt. II. p. 311, PI. IT.) refuse to give up the 

 genus Zoia ; but since Du Cane (Ann. of Nat. 

 Hist. III. 1839, p. 4-38, PI. XI. or Froriep's neue 

 Notiz. XIII. p. 5, fig. 10-13), has verified, with 

 Cancer maenas, the observations of Thompson, 

 and Rathke himself (fViegmann^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 Zoea, this wonderful metamorphosis of 

 the Brachyura can no longer be doubted. See 

 also Steenstrup, in the Oversigt over det kgl. 

 danslve Videnskabernes Selskabs Forhandlinger, 

 1840, p. 15, or Muller's Arch. 1841, p. 218 (Hyas), 

 and Goodsir, Edinb. New Philos. Jour. No. 65, 

 1842, p. 181, PI. III. 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 Zoea ; see PhiUppi, in 

 fViegmann's Arch. 1840, I. p. 184, Taf. III. fig. 

 7, 8 ; also Rathke, Ibid. p. 242, and, Danzig. 

 Schrift. loc. cit. p. 29, Taf. III. ; Steenstrup, loc. 

 cit. ; and Goodsir, loc. cit. No. 65, p. 182, PI. 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 Rathke, 

 Entwiclf . rt. Flusskr.) and in the Danzig. Schrift. loc. 

 cit. p. 23, Taf.' II. (Homarus) ; Du Cnne, Ann. of 

 Nat. Hist. II. 1839, p. 178, PI. VI. VII. or Fro- 

 riep's neue Nutiz. XIII. p. 3, fig. 4^-9 (Palae- 

 mon and Crnngon) ; Kroyer, Monogr. loc. cit. p. 

 37, PI. VI. (Hippolyte and Homarus) ; Joly, Ann. 

 d. Sc. Nat. XIX. loc. cit. PI. IV. (Caridina), and 

 Erdl, loc. cit. p. 18, Taf. III. IV. (Homarus). 



S According to Milne Edwards (Instit. 1838, 

 No. 25S, p. 397), a cephalothoro.x and abdomen 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 (Ann. d. Sc. Nat. III. 1835, p. 328, PI. XIV. 

 fig. 14). 



For the embryos of the Isopoda and Amphipoda, 

 see Rathke, Abhandl. loc. cit. ; Ann. d. Sc. Nat. 



II. 1834, p. 139, PI. XI. ; Zur Morphol. &c. 41, 

 Taf. II. III. (Bopyrus, Idothea, Janira, Lygia 

 and Amphithiie) ; Nov. Act. Nat. Cur. XX. p. 49, 

 Tab. I. (Phryxus) ; also Milne Edwards, Ann. d. 

 Sc. Nat. III. 1835, p. 323, PI. XIV. (Cymothoa, 

 Anilocra, Phronima and Amphithoe) ; finally 

 Rathke, in TViegmann^s Arch. 1839, loc. cit. Taf. 

 VI. (Mysis). 



"! See Gervais, Ann. d. 1. Soc. Entomol. de 

 France, 1837, and Institut. 1839, p. 22; IVaga, 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. 



