'njoriioni.AS'i' anh sjiiuosa. 007 



fast ill all(M\ hisluM' hcUaimt ^(nvordrncu I'^jlllcn, mid sic '^v- 

 laiij;t s(>ll)st. (lami zmu AiisdiucU, wciiii dcr Kcinisl icilrii iiii 

 Ul)rijj;('ii vollkommcn doi'snl i^ckriiinmt isl." 



I caiiuot follow llryiHoiis in tli(> iihovc compiirisoii hciwccu 

 tlic vontral (IcMirii of his Lcpisnia cMiihiyos and I lie candid 

 flexun^ ol otiicr ins(>ct (Muhrvos.' 



The embryos oC 1'. no v;e-l)rilai\ ni;c nnderj^o thriio 

 absolutely distinet vcnitial llexjiros, namely, ( 1) the primitive 

 ventral flexnre, (2) the caudal (lexnrc^, and (.'5) tlu^ eepha.li(! 

 flexure; the last-named flexure; not bciui; constant, it is very 

 important to note that there is no connection whatevcM' 

 between the primitive ventral flexure and the caudal 

 flex n re; (sec Fij;. .'5, a). 



The pi'iinitiv(; ventral (Icxnre serves the imincMliatc; |)urp<)sc 

 of rcl(>asin;^ the primitives streak, i. e. tin; principal ;;rowin}j; 

 j)()int of the embryo, from tlu; rest o( the cmbryonie; tract, so as 

 to enable it to continue its j^rowth indcpcndcMitly of the 

 trophic vesicle; and it also 8(M'ves the essential purpose; of keep- 

 ing the growing embryo, during its early stiij^cs, in as small a. 

 space as possible, in ordeu' to admit of the trophoblast coming 

 into contact with the uterine mucosa (the chorion intervening) 

 over as large an area as possible. The flexure of the (nnbryo 

 is sufliciently accounted for on such physiological grounds as 

 these. 



The occurrence of thrcM; v(;ntral flexures in the 

 embryos of 1*. n ovie-bri l an nia; cannot be; too strongly 

 emphasised. 



In the Myriapods the ventral flexure of the (Mubryo is an 

 essential and characteristic feature of tin; d(;velopm(;i:t, and is 

 to be considered in conmiction with the abs(;u(C of an amnion. 

 It tak(;s place at a very early stage in tin; (Miilo-^natha 

 (Fig. 2, I?), while! in the (!liile)poda il, is prece;ele:d by a dorsal 

 flexure. The ventral flexure; ol' the; JVIyriapoels (with spe;eial 

 reference te) the (Jhilejgnatlia) is epiite e)bvi()usjy te) be; ielcn- 



' It. is, however, e|ui1,e; |)()«»iljlc t,liJit,, in e;e;rtaiii cjihch, the; (;;iii(lal llrxiin; 

 and the primary ventral flexure might coincieic. 



