THE MALACOSTRACA 



segments. According to Hansen the latter number is, here as 

 elsewhere, the more primitive. The endopodite is flagelliform, and 

 the expedite has the form of a plate, the so-called "scale" or 

 " squama," probably of use in swimming. As a rule the first three 

 segments of the endopodite are enlarged and are counted with the 

 two (or three) segments of the protopodite as forming a five- (or six-) 

 segmented peduncle. 



The mandible has a " palp " of three segments, never biramous. 

 The oral edge of the mandible is more or less distinctly divided into 

 a "molar process" and an "incisor process," and between them is 

 armed with bristles or spines. An accessory blade, the lacinia mobiliSj 

 lying close to the cutting edge of the incisor process and apparently 



FIG. 85. 



Diagram of a generalised type of Malacostraca showing the " caridoid fades." a', antennule ; 

 a", antenna ; abd.xom, abdominal somites ; c, carapace ; e, eye ; r, exopodite of antenna ; md, 

 mandible ; mjcf, maxillula ; mx", maxilla ; pip, pleopods ; r, rostrum ; t, telson ; th.app, thoracic 

 appendages; roy>, uropods ; < and 9 indicate the i positions of the genital apertures in'the 

 male and female .sex respectively. 



formed by the enlargement of one of these spines, is found in some 

 of the orders, and is perhaps also a primitive character. 



The maxillulae have two endites and a "palp" of several 

 segments. According to Hansen, whose investigations on the 

 skeletal framework of the mouth-parts will be often referred to, 

 the two endites belong to the first and third segments of the 

 appendage, a small sclerite which Hansen supposes to represent 

 the second segment having no endite in connection with it. An 

 exite, in the form of a rounded plate, may be present ; according 

 to Hansen it belongs to the first segment. The maxillae are more 

 complex in form and the primitive plan of their structure is not 

 quite clear. Apparently there are two endites, each of which is 

 bifid, corresponding to the second and third segments, and a palp 

 of one or two segments. 



The thoracic appendages (Fig. 86) are all similar, none of them, in 

 the primitive type, being differentiated as maxillipeds. Each has a 

 protopodite of two segments, the coxopodite and basipodite, with, 



10 



