266 CLA YPOLE. [VoL. XIV. 
Crustacea are not convincing, as there is great variation in the 
degree of development of these appendages in different groups. 
In some the first antennae are larger and the second small or 
absent, and in others the reverse is true. The evidence from 
the lower forms is more reliable. Ray Lankester enumerates 
the different appendages found in that archaic type Apus, and 
indicates that the first antennae are always present while the 
second are sometimes absent and sometimes present, in the 
same species, and always missing in some species. As Apus 
is considered more generalized in its structure than any other 
crustacean, it is suggestive that the first antennae should be 
constant and the second the more variable. This immediately 
suggests an interesting explanation for the added pair of mouth- 
parts found in Anurida, originating from the tritocerebral seg- 
ment. On this basis they are a modified form of the second 
pair of antennae in the crustacean; and hence Anurida, includ- 
ing, without doubt, its allied forms, possesses an adult structure 
clearly homologous with the second antennae, the very impor- 
tant appendages of some crustacean heads. It is interesting 
in this connection that Hansen considers the musculature of 
the head of Machilis much more like that of the crustacean 
than that of the insect. 
Fig. 48 represents an Anurida just hatched. It can be 
seen to have many of the characters of the adult form; it 
is, however, perfectly white, showing none of the black pig- 
ment characteristic of the adult. The surface of its body is 
not as wrinkled and folded at this young stage, and the cuticle 
lacks the finely papillose surface found in the older specimens. 
The antennae are clearly four-jointed, as described by Ryder 
('86); the terminal joint is less pronounced, however, and some- 
times is not completely separated from the third. Instead of 
a third joint there exists only a constriction. The collophore 
is prominent; it originates by the fusion of the two appendages 
on the first abdominal segment. Young animals at this stage 
are very active, and may be found in large numbers in the 
same places as the eggs. Judging from the great variation in 
the size of the eggs at the time of hatching, there is a great 
variation in the size of the animal; this must be the case, 
