TOO JOURNAL OF SCIENCE, 
are present in Mysis, as well as in the Edriophthalmata, and 
they are formed in essentially the same way in all,—by plates 
which are developed on the basal joints of certain of the cormo- 
pods. In all these forms the young pass through a long meta- 
morphosis within these pouches. The liver is comparatively 
simple. There are no spermatophores, and the spermatozoa 
have tails. The Cumacea are regarded by Boas as a greatly 
modified offshoot from the Mysidacea ; and the amphipods and 
isopods are derived from an ancestral form somewhat like, but 
more primitive than the living Cumacea. 
As regards the position of the amphipods and isopods, Boas’ 
view is directly opposite to that which has been generally 
accepted ; as he regards these as the most highly specialised 
and divergent of the Malacostraca, instead of low and primitive 
forms. The conspicuous segmentation of the nervous system, 
the absence of a carapace, the sessile position of the eyes, the 
ereat number of similar somites, the worm-like shape of the 
body, and the elongation of the heart,—all seem at first sight to 
show that these forms are ancient and low. Boas points out 
that the nervous system gives no proof of a primitive condition, 
as there are as many independent ganglia in Mysis as there are 
in the sessile-eyed Crustacea. It is true that the heart is longer 
than it is in Mysis ; but there are only three pairs of ostia, and 
the length of the heart, as compared with that of the mid-body, 
is no greater than it is in Mysis. As the eyes are stalked in 
Nebalia, the nearest ally of the Malacostraca, all of the latter 
must have inherited stalked eyes from their phyllopod ancestors, 
and the sessile eyes of the Edriophthalmata must be due to 
secondary modification. So, too, regarding the absence of a ~ 
carapace. As the Malacostraca inherits this structure from the 
phyllopods, those forms in which it is absent must have lost it 
by secondary modification.. The same thing is true of the ab- 
sence of ascale on the antenna. There is, therefore, no proof 
that these animals are primitive ; and the many points of resem- 
blance to the Mysidacea which we have just. noticed show the 
close relationship between these groups. But as the Mysidacea, 
like the Euphausia and the decapods, have stalked eyes, a cara- 
pace, and a fused mid-body, exopodites in first maxillee, exopo- 
dites and palpi in second maxillee and on cormopods, and as a 
seventh abdominal segment is present, we must believe that the 
Mysidacea are the more primitive group, and the Edriophthal- 
mata their recently modified and highly specialised descendants. 
Boas believes that most of these differences are due to the 
fact that the Edriophthalmata have become adapted for running 
instead of swimming; and he thus explains the loss of the exo- 
podites of the cormopods, the strengthening of the endopodites, © 
the shortening of the abdomen, the loss of power in the pleopods, 
the flatness of the body and abdomen, the thickening of the in- 
tegument, and the loss of eye-stalks and of the antennary scale, 
The respiratory function of the pleopods he attributes to the loss 
of the carapace, and the thickening of the integument, 
