98 JOURNAL OF SCIENCE, 
The Decapoda natantia resemble the Euphausiacea in many 
conspicuous and highly important particulars. In these two 
groups alone, among the Malacostraca, we have a free-swimming 
nauplius; and in both the carapace of the larva is a great 
mantle. The abdomen is bent in both, and the integument is 
horny. The carapace, the abdominal appendages, the large tail- 
fin, and the pointed telson are alike in both. The endopodite of 
the first pleopod is a copulatory organ in the decapods as well 
as in the Euphausiacea; and spermatophores are almost universal 
in these two groups, while they are found in no other Malacostraca. 
The close relationship between these two groups can hardly 
be questioned ; nor is it difficult to show that the Euphausiacea 
are the primitive, and the Decapod the derived, form. In the 
presence of simple epipodites, and of a four-jointed palp on the 
first maxilla, the Penzeade are nearer to the phyllopods than 
Euphausia; but in all other respects Euphausia is the most 
primitive, and it shows its close relationship to the lower Crus- 
tacea by many characteristics, among which are the following :— 
The terminal joint of the cormopod is rounded and blunt, as it 
is in Nebalia, instead of being pointed, as it is in all the Mala- 
costraca except Nebalia. There are no specialized maxillipeds ; 
but the first cormopod is like all the others, as it is in Nebalia, 
and all the cormopods are furnished with exopodite and epipo- 
dite ; while in all other Malacostraca there are true maxillipeds ; 
and either the exopodites or the endopodites, or both, are 
absent on some or on all the cormopods. The antenna hasa 
well-developed exopodite; and in the young this is flabellum- 
like, and very similar to that of the adult Limnadia, or Estheria. 
This feature of resemblance to the lower Crustacea is shared by _ 
the young of the Decapoda natantia. The first maxilla has a 
large exopodite ; while this is rudimentary in the Decapoda and 
Mysidacea, the only other Malacostraca where it occurs at all, 
The pleopods are much like those of Nebalia: they are efficient _ 
swimming organs, and are provided with an appendix interna. 
The spermatozoa, like those of the phyllopods, are simple round 
cells without tails; and this is true of no other Malacostraca 
except the Squillas. 
While the Euphausiacea are thus seen to be very much like 
the phyllopods in so many important features, they are true — 
Malacostraca ; but they have deviated greatly from their phyl-- 
lopod ancestor, and have acquired a small carapace, differentiated — 
cormopods with long slender endopodite, small exopodite divided 
into shaft and flabellum, and an epipodite which is purely res- 
piratory. They also differ from Nebalia in the possession of 
that distinctively Malacostracan organ, a tail-fin, made up of a 
telson and a pair of swimmerets. 
The relationship of Nebalia to the Malacostraca on the one ~ 
hand, and to the phyllopods on the other, has long been recog- 
nised, and Claus has even gone as far as to hold that this form 
is atrue Malacostracan ; but Boas believes that it is neither a 
true Malacostracan, nor the phyllopod from which the Malacos- 
