558 



MYRIAPODA. 



segments, inclosed in their proper skin, were 

 now more elongated and very much en- 

 larged, and the new segments were further 

 developed as well as the germinal membrane. 

 The external tegument was more extensively 

 separated from the whole body, especially at 

 the posterior part, and the head was retracted 

 within it and bent on the under part of the 

 thorax. It was thus evident that this tegu- 

 ment was not of recent formation, that it 

 simply enclosed the animal as the whole had 

 been previously enclosed in the amnion, as is 

 proved by the circumstance that it extended 

 smoothly over the whole body, antennae and 

 legs, and did not follow the inflection or redu- 

 plication of the proper surface of the animal 

 like the true skin beneath it, but passed di- 

 rectly over the segments, and was simply pro- 

 truded or distended by the growth of parts be- 

 neath, as in the instance of the new legs (6). 

 Up to this period, therefore, observes Mr. New- 

 port, the young Jnlus must still be regarded as 

 in the embryo condition, although for a day or 

 two after bursting the amnion, it possessed 

 the power of locomotion and evinced some 

 developement of instinct. At its next change 

 of skin, when it enters what Mr. Newport 

 regards as the fourth period of its developement, 

 and when it has acquired fourteen pairs of 

 legs, it assumes for the first time a condition 

 analogous to the larva state of true insects on 

 bursting from the ovum ; the difference be- 

 tween the two being that the analogue of this 

 tegument of the embryo in insects is slipped off 

 at the bursting of the amnion on leaving the 

 shell, while that of the Myriapod is not thrown 

 off until some days after it has entirely left the 

 ovum. This embryo condition of the animal 

 will therefore explain the circumstance of its 

 first acquiring a slight power of locomotion, and 

 then remaining perfectly quiescent without 

 taking food to prepare for this change the 

 third period of its embryo life. 



The lower portion of the alimentary canal is 

 at this time distinctly visible through the new 

 segments, exhibiting a corrugated or folded ap- 

 pearance, an arrangement doubtless intended to 

 allow of its sudden extension at the period of 

 throwing off the skin and elongation of the seg- 

 ments. The colon is of a very dark colour and 

 exhibits its thickened peculiar structure with 

 its longitudinal muscular bands. Around its 

 posterior part, Mr. Newport observed an aggre- 

 gation of what appeared to be globular cells. 

 They seemed to be part of the organs of gene- 

 ration in the course of developement. At first 

 they were regarded as hepatic vessels, but this 

 Mr. Newport considers could hardly be the 

 case from the fact that each of these organs 

 directly enters the canal as a straight vessel, but 

 they might be vessels folded up to be unfolded 

 suddenly, as in the case of the alimentary canal. 



By the twenty-sixth day the young Julus 

 casts off the covering in which it had hitherto 

 been infolded, and enters the fourth period of 

 developement, having now seven pairs of legs 

 and fifteen segments to its body (Jig. 324). 



In this condition the antennae were found to 

 have become elongated by at least one-third of 



their original length, and exhibited six distinct 

 joints. The eye still consisted of a single ocel~ 

 lus, but this was now surrounded by a darke r 

 coloured portion of the tegument. The new 



Fig. 324. 



legs (b c) were equal in size and length to the 

 original ones, but were evidently more feeble. 

 The transverse markings on the seven anterior 

 segments (2-7) were very distinct, and the large 

 brown patch on the seventh segment was much 

 darker in colour. The whole body of the ani- 

 mal was considerably elongated. This was 

 produced chiefly by the extension of the new 

 segments (7 g) formed by the germinal mem- 

 brane at the posterior part of the seventh, and 

 which, in the early part of the last period, 

 seemed to form a single distinct segment co- 

 vered by the common tegument. The most 

 anterior of these segments (8), now the eighth 

 of the whole body, had acquired an extent 

 equal on its upper surface to the preceding seg- 

 ment, but was shorter on its ventral surface. 

 Like the preceding original segments it was 

 divided into two regions by a transverse de- 

 pressed line. The next segment in succession 

 to this, the ninth, had also become enlarged to 

 about one-third of the size of the eighth, and 

 was, like it, marked transversely. The next 

 four segments were each more developed than 

 in the preceding state, but not to so great an 

 extent as the others. The two remaining seg- 

 ments (14 15), the penultimate and anal, had 

 undergone no change. They had simply ac- 

 quired a little extension at the apex of the seg- 

 ment, and were now covered with a few scat- 

 tered hairs. It is thus proved that the body is 

 elongated, not by the division of the newly 

 formed segments into others, but always by the 

 formation of new ones in the germinal mem- 

 brane that extends from the posterior margin of 

 the antipenultimate segment to the penultimate, 

 which last segment, with the anal, undergoes no 

 change. That segment is always furthest ad- 

 vanced in growth which is immediately poste- 

 rior to the last segment that possesses legs, and 

 then the next in succession, until we arrive at 

 the terminal ones the penultimate and the 

 anal that never possess legs. 



By the forty-fifth day more new segments 

 had evidently been developed by the germinal 



