346 PROFESSOR E. RAY LANKESTER. 
second or third of another Arthropod B., and so on; but 
ambiguity is inevitably introduced if we attempt to indicate 
this homology by the use of such terms as antennule and 
antenna, to be applied in both cases alike, for in such cases 
as the parasitic Copepoda, the various Arachnida, and the 
living and fossil branchiate scorpions (Merostomata), these 
descriptive terms, and others like them, are found to be 
absolutely contrary to fact in their implications, and in- 
volve also debatable assumptions in reference to ancestral 
primitive forms. 
The first pair of appendages of Apus cancriformis may, 
therefore, be described as functional antenne. Hach con- 
sists of two segments, separated by a joint or soft ring of 
the chitinous cuticle, which allows the bending of one joint 
upon the other ; but there does not appear to be any muscular 
band entering the appendage in the adult Apus. A variable 
number (two to four) of sets’ are set upon the free end of 
the appendage. 
The second pair of appendages is alsoantenniform. Hach 
consists of a single filament, the base of which is attached 
to the under surface of the head, not far from the first. 
The filament is strongly curved but possesses no joint,” nor 
does any muscular fibre penetrate its axis. It tapers 
towards its free extremity which is setiform. Its total 
length is about one third of that of the first pair. 
In the adult Apus cancriformis and in Apus Duki, from 
Affghanistan (? 4. Himalayanus), this second pair of preoral 
appendages, although reduced to a rudimentary condition, is 
always present, so far as my observations go. I have found 
them always present in full-grown specimens of Apus can- 
criformis from Munich, from Prag, and from Padua. 
Their existence in the adult has recently been denied. 
Zaddach states that they are generally absent in A. cancri- 
formis, but were found by him in two cases; Huxley states 
that he was unable to find them in Apus glacialis examined 
' The sete of Crustacea are in distinction from the bristles of Chetopods, 
which are also often called “sete,” superficial prolongations of the con- 
tinuous chitinous cuticle which is produced by the epidermis, and are not, 
as are the bristles of Chetopoda, formed in open or closed follicles each as 
the cuticular excrescence of one specialised cell of the epiderm. It wouid 
be well to distinguish the follicle-formed sete of Chatopoda as ‘ chete ” 
or ‘‘ cheetomes.” 
? A comparison with Zaddach’s and Claus’s figures of Apus larve leads to 
the conclusion that the part of the larval second antenna which thus sur- 
vives is the base and short prowimal ramus (neither exopodite nor endo- 
podite); all beyond this forming the larger part of the larval antenna 
ppears to atrophy completely. 
a 
