Limbs and Mouth-parts of Crustaceans and Insects. 420 



logous "with the coxopodite in tlie Malacostraca (it resembles 

 the first segment of the leg of nMt/sis, but is, however, some- 

 what longer) ; the coxa therefore becomes homologous with 

 the basipodite. To the outer side of the coxse of the second 

 and third pairs of legs there is articulated a conspicuous 

 hairy " style," which is perhaps homologous with the exo- 

 podite (Wood-Mason). 



34. The abdomen consists of eleven segments (ten + the 

 telsori), a number which is met with again in the Cicadaria, 

 £phe7nera-\B.vvss, and other forms; according to Lacaze- 

 Duthiers it is the primitive number in the Insecta. The 

 well-known styles on the underside of most of the segments 

 are without doubt portions of rudimentary appendages, and 

 we may perhaps, on account of their position and agreement 

 in form with the styles of the thoracic legs, regard them as 

 exopodites (Wood-Mason). The triangular plates which 

 bear the styles, and from which the hindmost in particular, 

 especially in the case of specimens which are scarcely half- 

 grown, project backwards as somewhat large processes, I 

 consider with tolerable certainty to be homologous with the 

 stems of crustacean appendages (Wood-Mason), The styles 

 of the tenth segment constitute tiie well-known " cerci," 

 which are homologi;us with the cerci in other Insects. 



'65. In the Mysid^ and Araphipoda we find, as is well 

 known, four pairs of mouth-parts, and behind these fourteen 

 segments, of which the last is without appendages. I have 

 shown above that in the case of Marhilis the corresponding 

 four pairs of oral appendages exist, and behind them we also 

 find fourteen segments, the last of which is likewise devoid 

 of appendages. The tendency, wiiich in the Malacostraca is 

 of frequent occurrence, to develop the last pair of abdominal 

 feet in a peculiar manner and to retain these, while the five 

 preceding pairs undergo reduction (MysidjB, Cumacea), is also 

 met with in tiie case of Machilis and other Insects. 



/3. Campodea, Japyx, Collembola (§§36-39). 



36. In the formation of the head and the structure of the 

 mouth-parts these three types are very closely allied. They 

 are especially distinguished by the well-known peculiarity, 

 that the mandibles and maxilla?, with the exception of their 

 tips, " lie within tiie iiead." Tiiis has arisen in consequence 

 of the fact that the integument behind their points of inser- 

 tion has become folded forwards and around them, like a 

 reduplicature which contains tissues ; and on the underside of 

 the head the edges of this reduplicature have become firmly 

 united with the lateral margins of the labium, so that the 



