APPENDAGES AND NERVOUS SYSTEM OF APUS CANCRIFORMIS, 347 
by him, whilst Claus, whose statements have the very 
greatest weight, both on account of his extended investi- 
gation of the morphology of the Crustacea and of his special 
observations on the development of Apus and Branchipus, 
brings forward the total absence of the second pair of 
preoral appendages in Apus as a special characteristic of 
the family Apuside. He says, in the fourth edition of his 
‘ Grundziige der Zoologie,’ 1880, p. 527, ‘* Die Tastantennen 
sind kurz zweigliedrige Fadchen, die hintern, welche bei der 
Larve einen zweiastigen Ruderarm bilden, fallen ganz aus.” 
A similar statement occurs on p. 523. Gerstaecker offers 
no original observation on the subject, nor does he figure 
either the first or second pair of appendages of the Apus 
productus, which he has illustrated in his Pl. xxx, but con- 
fines himself to quoting the statement of Zaddach. 
The complete suppression of a pair of appendages is a 
matter of some importance, and in this particular case the 
presence or absence of the pair in question has a special 
interest in relation to the condition of that part of the 
nervous system by which they should be supplied. The fact 
is that, though rudimentary, the second pair of preoral 
appendages (so-called antenne) is present in the adult Apus 
of at least two species. 
Abdominal appendages: appendages behind the generative 
apertures.—It will be most convenient to pass next to the 
description of this group of appendages, since they appear to 
present the least specialised form of the whole series. 
It has been customary to regard the higher Podophthal- 
mata as a standard for the morphology of Crustacean 
appendages, and to interpret the parts seen in other Crus- 
tacea by reference to them, and to apply to those parts the 
analysis indicated in the terms protopodite (including coxo- 
podite and basipodite), endopodite, exopodite, and epipodite. 
When, however, the question is looked at from the point of 
view of evolutional morphology, there appears to be no 
ground for expecting that the analysis applicable to the 
special adaptations of the Podophthalmata should also be 
applicable to the lower Crustacea, and it will be best to 
consider the parts of the appendages of Apus merely in 
reference to one another and to the appendages of closely 
allied forms, deferring for the present the consideration of 
the homologies or agreements of these parts with those of 
widely separated forms. 
Taking the first post-genital appendage of the right side 
(seventeenth of the whole series), we find it to be a leaf-like 
plate attached by one end to the body, so that its flat sur- 
