Limbs and Mouth-parts of Crustaceans and Insects. 425 
logous with the coxopodite in the Malacostraca (it resembles 
the first segment of the leg of a Mysis, but is, however, some- 
what longer); the coxa therefore becomes homologous with 
the basipodite. T’o the outer side of the coxe 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 
telson), a number which is met with again in the Cicadaria, 
Ephemera-larve, 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 the well-known “ cerci,” 
which are homologous with the cerci in other Insects. 
35. In the Myside and Amphipoda 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, which 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 (Myside, Cumacea), is also 
met with in the case of Machilis and other Insects. 
8. 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 maxille, with the exception of their 
tips, ‘‘ le within the head.” ‘This 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 
