(Jajit. V. \V. lIiiftMU nri l\'ripatiis nova'-zcalaiidia'. 'M)7 



p^aniilar and yellow. A ^^cnninal vesicle and spot are deve- 

 lopecl in tlieni, and the ovum is plainly seen to be snrroiinde<l 

 ))y a clear vitelline substance enclosed in a distinct vitelline 

 membrane (IM. X\'1I. ti<;. {)). In an ovum •()(),S4 incli in 

 length the f^erminal vesicle was •(K)2 inch in diameter and the 

 •i^erminal spot •0005. The vitcllus now thickena and becomes 

 dark green by transmitted light, but white by reflected light ; 

 the germinal spot disappears ; and the ovum ap|)ears to be 

 hollow, and sometimes slightly constricted in the middle 

 (PI. XVII. tig. 10). 'J'herc is no micropyle. The ovum is 

 next detached trom the ovary; and the germinal vesicle dis- 

 appears, and the ovum passes into the oviduct. On passing 

 the vesiculos scminales it becomes fecundated, and total seg- 

 mentation ensues (PI. XVII. fig. 11) ; u tough hyaline enve- 

 lope, or chorion, now forms round the ovum. Owing to the 

 toughness of this chorion and the oj)acity of the vitellus, the 

 earlier stages of development are diliicult to follow ; but I 

 believe that it commences by a thickening of the blastoderm 

 at the head, which gradually extends backward, and the con- 

 tents of the ovum assume a rcniform shai)e. At a further 

 stage, when the embryo is sutticiently firm to be removed 

 from the chorion without injury, it is seen to be folded, with 

 the dorsal surface outward and the posterior flexure toward 

 the ovary. The formation of the limbs begins in front, and 

 extends backward ; they commence as hollow, slightly con- 

 stricted protuberances formed of two layers of cells (PI. XVII. 

 fig. 13, «). The intestinal canal is at first slightly extended 

 laterally towards the liollows of the legs. From the pro- 

 cephalic lobes bud off superiorly the antennaj (fig. 13, b), Aviiich 

 become ringed before the posterior leg-buds are formed. The 

 head is proportionally very large. The posterior extremity 

 is divided into two lobes (fig. 12), which ultimately form the 

 lips of the anus. At a rather later stage the opening of the 

 gullet is formed (fig. 14, d), and a trilobed growth is seen on 

 either side between the antenna^ and oral pa})ilUe (fig. 14, <■). 

 These, which are possibly homologous with a ])air of legs, al- 

 though tlu-y are developed later, subsequently grow inward 

 and form the sides of the mouth (figs, lo & 16, c). Two large 

 oval or pyriform swellings arise from the lower surface of the 

 cephalic lobes, just in front of t!ie opening of the gullet 

 (fig. 15,y) ; a longitudinal dej)ression is formed in each of 

 these by invagination | and in these depressions the teeth arc 

 subsequently formed. The under surface of the cephalic 

 lobes, just in front of these swellings, now grows downward 

 and covers them (figs. 15 & 10, 7), andsj^reads backward mitil 

 it unites with the frilo1)ed growth, jireviously mentioned, to 



