CRUSTACEA. 
341 
Norway. This part is confined to the families to which he has 
given the names Sidid^e and Holopedida5. After a general 
introduction, the author treats of the most important points in 
the organization of the Cladocera. 
The first which he desires to establish is the close rela- 
tionship of the Cladocera with the Phyllopoda. These two 
forms, which have hitherto been recognized as distinct orders, 
Hr. Sars contends, are united tlirough the Branchiopoda, 
which are distinguished from other Entomostraca bj^ hav- 
ing the organs of respiration attached to the feet, whereas in 
the other orders tliey are attached to the oral appendages. 
The union between these two orders has been thought by 
Professor Gmbe to be through the family Lynceidse; but 
Hr. Sars contends that the nearest approach is through the 
Sididse, in which the orgaiiization is more perfect than in any 
other family of the Cladocera, and which have the nearest re- 
semblance to the bivalve Phyllopoda, as Gimnetes, Estheria, 
Limnadia. 
He maintains that there is a very considerable analogy between 
the different groups of the Entomostraca and the great divisions 
of the Malacostraca, and points out, at the end of his general 
introduction (page 4), some of the most pronounced mutual 
affinities. 
Hr. Sars adopts the usual structural nomenclature, and names 
those somites that carry the antennje and oral appendages 
the head [cephalon], the part that carries the feet the thorax 
[pereion], the posterior part that carries no appendages the 
abdomen, and states that in most Cladocera there is a portion 
of the animal still posterior, that may be called ^^post-abdomen 
[pleon]. These terms, he says, are those proposed by Prof. 
Lilljeborg ; but this latter author has, in his recent com- 
munications in carcinology exchanged them for caput [ce- 
phalon], ^Gruncus'*^ [pereion], ‘^‘^cauda’^ [pleon]. In some 
genera these divisions are so distinctly visible that Hr. Sars 
thinks they at once demonstrate the desirability of their adop- 
tion in preference to those suggested by M. Leydig and 
certain recent carcinologists, since they are applicable not 
only to the Crustacea but also to the entire section of the 
Arthropoda. 
Hr. Sars coincides with the opinion of Prof. Milne-Edwards 
that the bivalve test of the Cladocera is the homologue of the 
carapace of the Decapoda, having undergone excessive develop- 
ment of the lateral walls. 
The author has given considerable attention to the pereiopoda, 
of which the construction is very complicated. He objects to 
the term feet being given to these appendages, as they do 
not assist in locomotion, while their chief functions are 
respiration and alimentation. He therefore thinks that, on 
