JlSU endoskeletal systems of scoepio. 



341 



Arthrodial Membrane. — The lateral part of the body and all the interspaces between 

 the sclerites are covered with a flexible membrane, the " arthrodial membrane " (am). 



Internal Skeleton. — The internal skeleton may be divided into two parts, the ento- 

 sclerites and the entochondrites. The entosclerites are epidermal in origin, and are 

 really only ingrowths of the external skeleton ; they may be divided into two kinds, 

 the coxal entosclerites, which are internal processes of the coxal sclerites of the 

 appendages, and the median entosclerites, which are continuous with the external 

 skeleton in the median line. The entochondrites are fibro-cartilaginous pieces which 

 are freely movable, not being fixed to any chitinous parts of the skeleton, and only 

 attached to them by fibrous tissue and muscles. They form a strong point of attach- 

 ment for muscles, which radiate from them to the appendages, tergites, and other parts 

 of the body. These skeletal pieces have been formed by a condensation of connective 

 tissue. 



Fig. 1. 



Fig. 1. Diagrammatic view of the anterior portion of a Scorpion (ButJius) divided along the median longi- 

 tudinal line, all the soft parts hoing removed so as to show the relations of the entosclerites (ingrowths 

 of the epidermic cuticle) and the entochondrite, which is alone shaded. (Compare PL LXXIX. fig. 15.) 



i, chelicera ; n, second appendage (chela) ; vn, vm, ix, tergal sclerites of the seventh, eighth, and 

 ninth segments ; A, coxal entosclerites of the chelicera ; H, preoral entosclerite ; K, postoral entosclerite ; 

 L, carino-sternal entosclerite ; Cam, camerostome (upper lip) ; vn gc, sternal region of the genital seg- 

 ment ; vm nee, pecten ; ap, left anterior process of the great entochondrite attached to the left arm of 

 preoral entosclerite ; ent, body of the great entochondrite ; Snp, subneural arch of the same ; nc, neural 

 canal of the entochondrite ; gc, gastric canal of the entochondrite ; nf, posterior flap or fibrous expansion 

 of the entochondrito spread out as a diaphragm across the body ; arc, arterial canal ; Ent", second ento- 

 chondrite (suprapcctinal). 



Coxal Entosclerites (PI. LXXIX. figs. 15, 16). — The coxal entosclerites are called 

 either anterior or posterior, according to the portion of the interior margin of the 

 coxal sclerite on which they are situated. 



