CRUSTACEA. 415 



The males are smaller, sometimes even dwarfed, and then attached 

 to the females like parasites. They almost always possess appa- 

 ratuses for holding the females and for transferring the spermaio- 

 plmres during copulation. The larger females, on the other hand, 

 frequently carry the eggs about with them in sacs, the membranes 

 of which are secreted by the so-called cement glands. 



Development takes place either directly or by metamorphosis. 

 The metamorphosis is sometimes retrogressive. When the develop- 

 ment is direct, the young animals, on leaving the egg, already have 

 the body form of the adult. The larva known as the JWauplius 

 (fig. 332) is of great importance as a point of departure. This 

 larva possesses an oval body, on the ventral side of which are present 

 three pairs of appendages for the sense of taste, the prehension of 

 food, and for locomotion. These appendages correspond to the two 

 pairs of antenna? and mandibles respectively. Parthenogenesis is 

 said to occur in certain groups (P1>i/Uo- 

 poda). 



Almost all Crustacea are carnivorous. 

 Some of them suck the juices of living 

 animals on which they are parasitic. 



For the systematic review of this 

 heterogeneous group, it is convenient to 

 divide the numerous orders into two 

 series. 



1. The small simply organized Cms- Pl& . - 332 ._ Naaplius Iarva of 

 tacea, the number and form of wlm-i- Snimms, seen from the side. 



T . -11 i A First appendage (first an- 



appendages is very various, will be in- teima);^ second appendage 



eluded as EntOmOStraca (O. Fr. M tiller). (second antenna) ; Mdf, third 



,1 j Til 77 appendaqre (mandible); Ob, 



To this group belong the orders Phyllo- upper lip ; z>, intestine. 



, Ostracoda, Copepoda, and Cirripedln . 



2. The higher Crustacea, characterised by a definite number of 

 segments and appendages, may be grouped together as Malacostraca 

 (Aristotle). In this group are included the orders of Arthrostraca 

 (Amphipoda and Isopoda], and Thoracostraca ((_'utcff( Sf<>/n<tf<ij>f/ri. 

 Schizopudn, and Decapoda\ 



In addition there is the genus Xi'l>l!. which has been hitherto 

 erroneously placed with the Phyllopoda, but which is to be regarded 

 as the representative of an ancient group connecting the PJij/llopoda 

 with thf Miili-uxf,-t-<i. and may be opposed to the latter as Lept- 

 ostraca. ' 



Finally, in addition to these chief divisions, there is a number 



