556 



MYRIAPODA. 



Fig. 321. 



investment, either adipose or peritoneal, except 

 only what belongs to itself; but is closely sur- 

 rounded by cells of the second and third size. 



On the tenth day the great circulatory or 

 dorsal vessel was distinctly seen through the 

 amnion and skin. This doubtless had existed 

 much earlier, although not observed. It was 

 exceedingly well marked, but Mr. Newport was 

 as yet unable to detect any motion in it. The 

 head of the embryo had now begun to assume 

 the peculiar corneous appearance common to 

 the larvae of true insects; its body had much 

 increased in size, and the amnion was still co- 

 vered with microscopic drops of fluid. 



On the eleventh dai/ the head was more dis- 

 tinct, and the antennae appeared at its sides 

 like short crescent-shaped clubs, with their 

 terminations directed forwards. Above them 

 the single ocelli were distinctly seen. All 

 the segments, posterior to the third, exhibited 

 the transverse line that indicated the division 

 into double segments, and the posterior seg- 

 ments were much increased in size. 



On the morning of the seventeenth day (Jig. 

 321) Mr. Newpoit found all the embryos ready 

 to leave the amnion. 

 Some of them were al- 

 ready detached from the 

 shell ; others were still 

 connected to it. Their 

 increase of bulk within 

 the last few hours had 

 been very great. The 

 body was now more 

 straightened, the head 

 less inflected under the 

 thorax, and the eye was 

 a dark-coloured spot 

 above and behind the 

 antennae. The segments of the body were di- 

 vided by distinct reduplicatures of the proper 

 tegument, and the legs folded side by side 

 against the ventral surface were much further 

 extended beneath the amnion (l>, ). The trans- 

 verse divisions of the first six segments strongly 

 marked the original segments, and the amnion, 

 now about to burst, was tightly extended over 

 the dorsal surface, and by the elongation of the 

 body was rendered more distinct on the ventral. 

 The great increase in the length of the animal 

 was mainly occasioned by the growth of the 

 posterior segments, more especially those in 

 the antepenultimate space, the proper germinal 

 space or membrane (./'), the faint divisions of 

 which into new segments were now distinctly 

 seen through the amnion. The seven anterior 

 segments, including the head, were greatly en- 

 larged, and the hitherto minute anal and pe- 

 nultimate segments (8, 9), in the first of which 

 the remains of the funis (d) forms a rudimen- 

 tary spine, had also become enlarged, and were 

 now fast acquiring the form they afterwards 

 retain throughout the life of the animal. Some 

 of the specimens soon threw off their covering 

 and entered the third period of development. 



The animal was now greatly enlarged, and 

 possessed three pairs of legs, but it still lay 

 with these newly developed legs coiled up 

 without voluntary motion. The amnion had 



been fissured at its anterior dorsal surface, and 

 slipped oft" backwards from the posterior seg- 

 ments, and lay at the anal extremity, while the 

 animal itself, with its limbs coiled up, appeared 

 as if exhausted with these its first spontaneous 

 efforts. No other signs of animal existence 

 were given than occasional slight movements 

 of the antennae. The embryos thus passed 

 from their apparently inanimate to an animated 

 state of existence, from a condition in which 

 they appeared merely to vegetate, endowed 

 with no voluntary or instinctive powers, but 

 like the vegetable formed entirely of an aggre- 

 gation of cells, totally incapable of spontaneous 

 motion, to one in which they became active 

 beings, gradually acquiring voluntary and in- 

 stinctive faculties both as regards the means 

 of procuring nourishment and of preserving 

 themselves from injury. 



In about an hour after leaving the amnion 

 the young Julus exhibited a marked change. 

 Its head was elongated on the prothorax (2), 

 the parts of the mouth were distinctly move- 

 able, and the eye, a single ocellus on each side 

 of the head, acquired a darker colour. The 

 whole body had been increased at least one- 

 fourth in bulk since leaving the amnion. It 

 now measured about a line in length, and ex- 

 hibited very distinctly the nine original seg- 

 ments. The seven anterior of these were 

 strongly marked. In the germinal apace, (Jig. 

 321,^/j) between the original seventh and eighth 

 segments, six new segments were now developed. 

 These were still very small, the length of the 

 whole being equal only to that of one of the 

 original segments. At the present time they 

 did not form independent divisions of the body, 

 but were covered by the common tegument, and 

 thus appeared like supplementary parts of the 

 seventh segment produced from the germinal 

 membrane and interposed between the seventh 

 and the penultimate segment (8), which, as be- 

 fore stated, is a permanent segment throughout 

 the life of the animal. This latter fact shews that 

 it is not merely by an elongation and division 

 of the terminal segment that the body of the 

 Julus is developed, but that it arrives at its per- 

 fect state by an actual production of entirely 

 new segments ; that these are new growths or 

 formations which are in progress long before 

 they are apparent to the eye, and that the 

 original segments of the ovum into which the 

 animal is first moulded are permanent segments 

 throughout its whole life. 



But still more curious is it that not only have 

 new segments been formed as described, but 

 that the common tegument by which they are 

 now covered and which also invests the whole 

 body as the true skin, has already begun to be 

 detached preparatory to its being thrown off, as 

 is shewn in the fact that the new segments are 

 now seen beneath it ; and it is further remark- 

 able that this deciduation of the first skin of 

 the animal had actually commenced before the 

 bursting of the amnion. These circumstances 

 explain the cause of the very quiescent state of 

 the young Julus, and its almost and perhaps 

 entire abstinence from food whilst this skin 

 remains on its body. It is not until this skin 



