96 JOURNAL OF SCIENCE. 
THE PHYLOGENY OF THE HIGHER CRUSTACEA® 
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BY W. K. BROOKS. 
a Qe ee 
The class Crustacea is one of the dominant groups of the 
animal kingdom, and it includes a very considerable propor- — 
tion of our living animals. Its representatives are extremely ~ 
diversified in structure ; and a single order, such as the Decapoda, 
includes a much greater variety and diversity of forms than the 
whole class of insects. It is very rich in primitive and transi- 
tional forms ; and when we add to this that there is no groupin 
which our embryological knowledge is more rich and varied, or 
in which the embryological history of the individual throws so 
much light upon the evolution of the race, its importance as a 
means for tracing the actual history of the evolution of species 
is obvious. In fact, most of the problems in the logic of morpho- 
logical reasoning, are, in great part at least, problems in the 
morphology of the Crustacea. 
Since the awakening in natural science which followed the 
publication of the “Origin of Species,’ many naturalists have 
attempted to disentangle the story of the phylogeny of the Crus- 
tacea. Some of these attempts, such as Miiller’s “ Fiir Darwin ” 
and Huxley’s “ Crayfish,” are familiar to all; while others, such 
as Claus’ “Crustaceen System,” are known to none except 
specialists. The latest attempt in this field (“Studien iiber die 
verwandschaftsbeziehungen,” by Dr. J. E. V. Boas, Morph. 
Fahrb., viii. 4, 1883) is, to say the least, a very valuable addition 
to crustacean morphology, as well as an interesting study in 
scientific logic. Its results seem to be a close approximation to 
the true natural classification of the higher Crustacea, and it 
should therefore receive the careful attention of all naturalists, — 
and of all who wish to be informed regarding the methods of — 
thought in morphology ; but, as it is from necessity filled with 
minute details, which would be formidable to all except specialists, — 
the general reader must be contented with a summary of the 
results. 
The proof that the crabs are descended from long-tailed de-. 
capods is familiar to all naturalists ; and no one can doubt, that, — 
among these, the swimming decapods, such as Penaeus, are the 
most primitive. So far, the phylogeny of the decapods may be 
regarded as definitely settled, and Boas proposes no modification — 
of the accepted view; but his opinion regarding the origin of — 
the swimming decapods from the lower Crustacea is novel, and 
the evidence which he furnishes seems to be conclusive. The 
Decapoda are generally regarded as the modified descendants of 
the Schizopods ; but Boas points cut that the order Schizopoda 
is not a natural group, since the animals which have been in-— 
cluded in it belong to two widely separated orders. j 
* Extracted from ‘‘ Science,” Vol,II., p. 790 (December 21, 1883). 
