MYEIAPODA. 



defined space, that unites the seventh and eighth segments into one mass ; 

 but in proportion as the anterior parts of the body become developed, 

 this part is also enlarged, not as a single structure, but as a multiplica- 

 tion or repetition of similar structures. 



(735.) About the seventeenth day the little embryo is ready to leave 

 the amnion in which it has been hitherto enveloped. Its body is found 

 to have become considerably elongated, the increase of length being 

 mainly occasioned by the growth of the posterior segments, but more 

 especially by the development of new ones, which now begin to make 

 their appearance in the antepenultimate space (fig. 141, c, /), which is, 

 in fact, the proper germinal space or germinal membrane, whereby the 

 production of all the future segments is effected. The seven anterior 

 segments, including the head, are now greatly enlarged, and the hitherto 

 minute penultimate and anal segments (8, 9) become much enlarged, and 

 rapidly acquire the form they afterwards retain through the life of the 

 animal. This latter fact shows that it is not merely by an elongation 

 and division of the terminal segment that the body of the Julus is de- 

 veloped, but that it arrives at its perfect state by an actual production of 

 entirely new segments, the formation of which is 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. 



(736.) The manner in which new legs are produced is equally curious. 

 Up to the present period the animal is furnished with only three pairs 

 (fig. 141, c, 6 c), but four additional pairs are nevertheless in progress 

 of formation. These, at present, exist only as eight minute nipple- 

 shaped prominences on the under surfaee of the sixth and seventh seg- 

 ments (fig. 141, c, 6, 7), four on each, covered by the common integu- 

 ment, which, as in the larval condition of insects, is a deciduous mem- 

 brane. The newly-formed legs, however, go on rapidly increasing in 

 size until about the twenty-sixth day, when, throwing off the skin in 

 which it has hitherto been encased, the young Julus presents itself 

 with seven pairs of legs and a body consisting of fifteen segments 

 (fig. 141, E). 



(737). In this condition the body of the animal still continues to 

 elongate, not by the division of the already-formed segments into others, 

 but always by the formation of new ones in the germinal membrane 

 that extends from the posterior margin of the antepenultimate segment 

 to the penultimate, which last segment, as well as the anal, undergoes 

 no change ; and it may likewise be observed that that segment of the 

 newly-formed portion of the body is always furthest advanced in growth 

 which is immediately posterior to the last segment which possesses 

 legs, and then, the next in succession, until we arrive at the terminal 

 ones (the penultimate and the anal), that never have legs appended to 

 them. 



(738.) On again casting its skin, the new segments of the body pro- 



