Common Crayfish. 97 



velopraent of the 'telson^ in particular^ p. 27, and ' Zur Mor- 

 phologies Reisebemerkungen aus Taurien/ 1837, pp. 113-115. 

 In this latter work about fifty pages are devoted to general 

 remarks on the development of Crustacea. 

 For the development of other Crustacea, see Spenee Bate, Phil. 

 Trans., 1858; Fritz Miiller, Archiv. fiir Naturgeschichte, 

 1862, 1863; Van Beneden, Recherches sur la Faune Lit- 

 torale de Belgique, Crustaces, 186 1 ; Claparede, Beo])aeh- 

 tungen iiber Anatomic und Entvvickelungsgeschichte wirbcl- 

 loser Thiere, 1863, lUque citata. 

 For the morphology of the appendages, see Savigny, Memoires 

 sur les Animaux sans Vertebres, 18 16, vol. i., p. 4S, Mem. ii., 

 pi. iii. and iv. ; Erichson, Entomographien, 1840, where, at p. 

 28, attention is drawn to the fact of the relative prominence of 

 the thoracic appendages in the larval (Zoea) stages of Crustacea 

 which undergo metamorphosis, and to the illustration which 

 this peculiarity in the development of Crustacea affords of 

 their essential affinity to other Arthropoda which possess the 

 same hexapod arrangement permanently as adults in the class 

 Insecta, or, it may be added, pass through a hexapod larval 

 stage, as lulus among Myriapoda, and Hydrachna among 

 Arachnida. That the prolegs of Insect larvae are rightly con- 

 sidered as homologous with the abdominal and post-abdominal 

 limbs of Crustacea, though the proleg, even when greatly elon- 

 gated as in the anal appendages of the Puss Moth {Cemra 

 Schrank), is still an annulated rather than a segmented and 

 articulated outgrowth, may be seen from the fact that prolegs 

 and true legs may replace each other. In the Coleopterous 

 Insect Sjnrachtha Eurymedusa, described by Schiodte in the 

 Ann. Sci. Nat., Ser. iv., torn, v., 1856, p. 178, pi. i., fig. 19^ 

 we have the first, second, and third prolegs of the Lepidop- 

 terous larva replaced by biarticulate appendages ; whilst in the 

 Coleopterous CurcuUonidae we have the thoracic legs replaced 

 by prologs. 

 For excellent figures of the appendages, see Brandt and Ratzcburo-, 

 ' Medizinische Zoologie,' Bd. ii., Taf. xi., p. 58; or, Victor 

 Carus, ' Icones Zootomicae,' Taf. xi. 

 See also Milne-Edwards, 'Suites a BufTon/ Crustaces, torn. i. ii. 

 iii., and in ' Regne Animal,' Crustace's, Atlas, pi. iv. 



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