284 



MYEIAPODA. 



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in the earth or vegetable mould in which the Julus is usually met with. 

 When first hatched, the young Myriapod is of course exceedingly dimi- 

 nutive ; at that period it resembles a microscopic kidney-bean, and is 

 completely destitute of legs or other external organs. After a few days 

 the embryo Julus changes its skin, and, throwing off its first investment, 

 appears divided into distinct segments, and furnished with a head, a pair 

 of simple eyes, a pair of antennae, and six jointed legs attached to the 

 anterior rings of the body (fig. 140, B, c). Some days subsequent to it 

 first moult, the skin is'again 

 cast, and the millepede, ac- 

 quiring larger dimensions, is 

 seen to possess seven pairs 

 of ambulatory extremities, 

 which are, however, still 

 placed only upon the anterior 

 segments (fig. 140, D). When 

 twenty-eight days old, they 

 again throw off their outward 

 covering, and assume, for the 

 first time, their adult form : 

 they then consist of twenty- 

 two rings, and have twenty- 

 six pairs of feet; but, of 

 these, only the eighteen an- 

 terior pairs are used in pro- 

 gression. At the fourth moult 

 the number of legs is in- 

 creased to thirty- six pairs ; 

 and at the fifth, at which time the body becomes composed of thirty 

 segments, there are forty-three pairs of locomotive organs. At last, in 

 the adult state, the male has thirty-nine and the female sixty-four rings 

 developed ; but it is not until two years after this period that the sexual 

 organs appear and the animals become capable of reproduction. 



(732.) The development of the young Julus has been traced more 

 recently by Mr. Newport with great care ; and the result of that gentle- 

 man's observations relative to this part of the history of the Myriapods 

 is of extreme interest, both to the physiologist and in an entomological 

 point of view. 



(733.) The embryo, when it first becomes distinguishable in the in- 

 terior, of the ovum, is entirely destitute of limbs, or of any appearance 

 of segmental division, and even at the moment of its escape from the egg, 

 which is effected by the laceration of the egg-shell, but very faint traces 

 of segmentation are discernible. After its extrusion, however, its growth 

 advances with considerable rapidity, a.nd it soon becomes visibly divided 

 into eight distinct segments, including the head (fig. 141, A) the ninth 



Growth of young Julus terrestris. (After De Geer.) 



