Lirnbs and Mouth-parts of Crustaceans and Insects. 427 



fourth phis the fifth in the case of the previous division / no 

 marsiipium ; motile larvce, lohich in the case of the lower forms 

 have a Nauplius stage and a large series of ecdyses ; a short 

 heart; no processes for the orifices of the vasa deferentia ; and, 

 lastly, hy the possession of spermatophores . The third group 

 is constituted by the Stomatopoda, which agree in some ot" 

 their characters with the first and in others with the second 

 division, but in various other respects occupy a very isolated 

 position. 



in. INSECTA. 

 a. Machilis (^§§28-35). 



28. The mandibles of Machilis are homologous with those 

 of the ]\lalacostraca ; in form they resend)le those of the 

 Cumacea, having a ivell-developed almost cylindrical pars 

 nwlaris, though they are without a lacinia mobilis | in articu- 

 lation and muscidoture they exhibit a surprising agreement 

 icithj e. g., Diastylis and Nehalia {vide also § 37), and herein 

 diverge to the utmost extent from, e. g., Orthoptera and Coleo- 

 ptera. 



29. The maxillai are composed of three segments and an 

 eight-jointed palpus. The basal segment [cardo) has no 

 masticating-lobe ; the second segment is produced into a long 

 lobe, which is transversely segmented at the tip ; the third 

 segment is also produced into a lobe {galea) and the palpus 

 arises from its outer side. The structure of the maxillLe{\\'\nc\\ 

 may be very easily examined in a preparation which has been 

 cleared with potash), as regards the origin of the lobes from 

 the second and third segments, consequently agrees precisely 

 with that of the viaxillre of the Eumatucostraca, while, on the 

 other hand, it is totally dijferent from that of the maxillulce. 



30. Jn the Isopoda (see a figure in " Cirolanidaj ") and 

 Amphipoda we find that the maxillipedes are situated very 

 close together in the median line, and, moreover, in the latter 

 order their first (or first and second) joints become fused 

 together ; the maxillai are articulateil in front and at some 

 little distance from the median line, while the maxilluUe are 

 attached somewhat further still from the median line, and the 

 hy]X>pharynx projects between and before their points of 

 articulation ; lastly, the mandibles are inserted far away from 

 the median line, obliquely outside and above the maxillulai 

 and niaxillaj. We meet with a similar arrangement of the 

 mandibles, maxillae, and labium in Machilis and, e. g., also 

 in the Orthoptera and Coleoptera. 



31. / regard the maxilla; in Machilis (^vide §§29, 32, and 

 39) as decidedly homologous ivith the maxilla: {second pair of 



