$2 MYRIAPODA chap. 



tube, which in the male is connected with accessory glands, and 

 in the female is usually provided with double receptacula 

 seminis. The generative openings usually lie near the base of 

 the second pair of legs (Ohilognatha), or at the posterior end of 

 the body (Chilopoda). In the Ohilognatha there is usually in the 

 male an external copulatory organ at the base of the seventh pair 

 of legs, remote from the genital opening. 



The preceding account of the anatomy of the Myriapods has 

 shown us the general characteristics of the whole group. I shall 

 now take each of the five Orders into which the class is divided 

 in the classification adopted in this account, and endeavour to 

 explain the differences in anatomy which have led to the estab- 

 lishment of the Order. The first Order with which we have to 

 do is that of tlie Ohilognatha, which includes a large number of 

 Myriapods ; no less than eight families, some of them including 

 a great number of forms. 



Order I. Ohilognatha. 



The Ohilognatha differ from other Orders in the shape of the 

 body. This is in almost all cases, cylindrical or sub-cylindrical, 

 instead of being more or less flattened as in the other Orders. 



The body, as in all other Myriapods, is composed of segments, 

 but in the Ohilognatha these segments are composed, in almost 

 all cases, of a complete ring of the substance of which the 

 exoskeleton (as the shell of the animal is called) is composed. 

 This substance is in the case of the Ohilognatha chitin (a kind 

 of horny substance, resembling, for instance, the outer case of a 

 baetle's wing), containing a quantity of chalk salts and colouring 

 matter ; the substance thus formed is hard and tough. In other 

 Orders the chitin of the exoskeleton is without chalky matter 

 and is much more flexible. The length of the body, as may be 

 seen from the classification, may be either very long, as in Jul'us, 

 or very short, as in Glomeris. 



The next anatomical character distinctive of the Order is 

 the form of the appendages. First, the antennae. These are, as 

 a general rule, much shorter than in the Ohilopods, never 

 reaching the length of half the body. They are, as a rule, club- 

 shaped, the terminal half being thicker than the half adjoining 

 the body. 



