Common Crayfish. 113 



anatomy of the antennae and jaws in Arthropoda, pi-ove that they are 

 appendages in just the same sense as any of the ventrally placed append- 

 ages attached to segments posterioi' to the cephalic ; and with them, 

 most authors, with the exception of Claus and Fritz Miiller, Avould be 

 inclined to rank the eyes. The facts of the pedunculation of these organs 

 in the Podophthalmatous, and indeed in some other Crustacea ; of the 

 occasional replacement of their facets by a flagellum such as the antennae 

 carry ; of their having a separate pair of lobes developed in connection 

 with them in the supra-oesophageal ganglionic mass in ordinary De- 

 capods, as shown by Eathkey, see p. io8, supra, in Amphipoda, and also 



y Bruzelius, Archiv. flir Naturgeschichte, torn, xxv., 1859, p. 306 ; Beitrag zur 

 Kenntniss vom innern Baue der Amphipoden, has described the supra-oesophageal 

 mass of an Amphipod, AmpMthoc Podoceivides, as consisting of three pairs of ganglia, 

 the most anterior of which is in relation with the eyes, the middle one with the 

 antennules, and the one nearest the mouth with the antennae. Similarly iVIr. 

 Newport, Phil. Trans., 1834, p. 422, pi. xvii. fig. 40, a, b, c, has figured and de- 

 scribed the supra-oesophageal nerve-mass in the common Lobster, Homarus Vulgaris, 

 as consisting of three pairs of ganglia in relation with the three pairs of sensory 

 organs specified. Though no air-breathing Arthropod has at any one period of its 

 life more than a single pair of antennary organs, Ratlike's figures of the cerebroid 

 mass in the developing Scorjiion, Morphologie, Reise nach Taurien, Taf. i. fig. 10, 

 and his description of it in contrast to the brain of the adult animal, as ' composed 

 of several pairs of ganglia lying one behind the other,' and also Metschnikow's 

 figures, Zeitschriffc fiir Wiss. Zool., Bd. xvi. Taf. xxx., figs. 31, 33, though not his 

 description of the brain in Aphis Rosae, lead us to think that the brain, even in 

 these classes, may make its first appearance as a bilaterally trilobed mass, indicating 

 thus the presence of three prae-mandibular segments. 



Mr. Newport indeed has put on record, Phil. Trans., 1843, p. 245, an observation 

 to the effect that in the embryo of a Chilopodous Myriapod, Geophilus Longicornis, 

 the brain is at the moment of its bursting its shell composed of four double ganglia. 

 But here it is probable that one of the p;iirs, as Metschnikow I. c. has shown to be 

 actually the case in Aphis Rosae, corresponded to the ' lobi optici,' whicli are lateral 

 outgrowths of the cerebroid ganglia, and do not therefore indicate the presence of a 

 separate segment, though they may have been displaced inwards by lateral com- 

 pression. See Leydig, Vergleich. Anat., p. 183. The brain in adult Myriapoda is 

 very obviously quadrilobular, as has been noted, by Newport, luce, citt., of Seulopendra, 

 Polydesmus, Geophilus Suhterraneus when adult, and by Zaddach of Lithohius Forfi- 

 catus. This point is particularly well shown in the brain of Glomeris Marginata, a 

 Myriapod closely resembling the Oniscus in external appearance. It has been 

 figured by Brandt, Miiller's Archiv., 1837, Taf. xii. fig. 7, p. 324, as consisting of 

 two irregularly quadrangular masses, prolonged at either outer angle into ocular 

 and antennary nerves respectively, and united at either inner angle to each other by 

 commissures passing over the oesophagus, and inclosing a wide ojiun space between 

 them. For the development of the prae-oral ganglia in Astacus, see Uatlike, Fluss- 

 krebs, p. 50. For the segmentation of the head, Kalhke, Morphologic, pp. 1 26, 



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