Tee PHYLOGENY OF THE HIGHER CRUSTACEA. 97 
According to this author, the Euphausiacea and the Mysida- 
cea are not atall intimately related. Thelatter are not in the 
line which leads to the Decapoda, and there is no natural group 
Schizopoda. He therefore divides the group into two orders,— 
the Euphausiacea and the Mysidacea : the former including the 
primitive unspecialised forms through which the Decapoda have 
been evolved from the lower Crustacea ;. and the latter containing 
highly specialised forms, which have been evolved from the Eu- 
phausiacea along an independent line, and which have no direct 
relationship to the Decapoda. He holds that the Euphausiacea 
are a synthetic group of crustacea which has given rise to several 
divergent groups of descendants. Of these the decapod stem 
has undergone the least modification. A second stem, the My- 
sidacea, has diverged in an entirely different direction, and has, 
in its turn, given rise to the Cumacea, and through these to the 
Amphipods and Isopods, the latter being the most highly modi- 
fied of the Malacostraca. A third line of descent from the 
Euphausiacea has given rise to the Squillacea. 
The recognition by Boas of the fact that the group Schizo- 
poda is not a natural one, and the discovery that the animals 
which have been thus associated may be divided into a very 
primitive group, the Euphausiacea, and a highly specialised 
group, the Mysidacea, seems to be a very great advance in crus- 
tacean morphology. He gives the following definition of the 
Euphausiacea :— 
Malacostraca, with the mid- body and abdomen compressed, 
with a well-marked bend in the abdomen; carapace well de- 
veloped ; the last segment of the mid-body a complete ring ; 
eyes stalked ; antenne with a large scale; mandible simple; 
first maxilla with broad, one-jointed palp, and with well-deve- 
loped exopodite ; second maxilla with a similar palp, and with 
exopodite, and a cleft lacinia interna. The appendages of the 
mid-body or cormopods all have a well-developed exopodite, 
and an epipodite which is subdivided in all except the first pair, 
where it is simple. The endopodite is thin and weak, and it 
does not end ina sharp point: it is more or less rudimentary on 
the last two pairs. The first cormopods are not specialized as 
maxillipeds, but are like the others. The abdominal feet are 
powerful swimming organs, with an appendix interna. In the 
male the first or most anterior ones are specialized as copulatory 
organs. The tail-fins are well developed. The liver is com- 
posed of a great number of small lobes. The heart is short and 
wide. The halves of the reproductive organ are united by a 
transverse unpaired portion. Spermatophores are present, and 
the spermatozoa are simple round cells. There is an antennary 
gland. The young leaves the egg as a free-swimming nauplius, 
and the carapace of the older larva is a great phyllopod-like 
mantle. 
It is easy to trace the relationship between this group and the 
decapods, on the one side, and, on the other side, through Ne- 
balia, to the Phyllopods and lower Crustacea. 
