1 50 WHEELER. 



EXPLANATION OF PLATE L 



i^Xiphidium atsifermn, Scud.) 



Fig. I {A). Surface view of embryo during gastrulation. p.o., indusium ; 

 pel, procephalic lobe; bl., blastopore; a., anal bifurcation of the blastopore; 

 ams., amnioserosal fold. 



Fig. 2 {B). Surface view of embryo with amnioserosal fold closed over trunk- 

 region, pcl.n., neuroblast-centres on the procephalic lobes. 0., anterior widening 

 of the blastopore. Remaining letters as in Fig. i. 



Fig. 3 (C). Surface view of embryo with the amnioserosal fold encroaching 

 on the indusial thickening ; po.am., amnioserosal fold of the indusium ; z., pedicel 

 temporarily uniting the indusium with the head ; at., antenna ; md.s., mandibular 

 segment; mx.s.,'^ first maxillary segment; mx.s.^ second maxillary segment; 

 p.s.,^-p.s.,^ first to third thoracic segments ; a.s.,^ first abdominal segment. Re- 

 maining letters as in Fig. i. 



Fig. 4 (Z>). Surface view of embryo just after the separation of the indusium 

 from the head. Letters as in Figs. 3 and i. 



Fig. 5 {E). Indusium spreading over the yolk. View of embryo nearly 

 completely submerged in the yolk, on its way to the dorsal surface, tc.s., 

 tritocerebral segment. Other letters as in preceding figures. 



Fig. 6 {F). Surface view of elongate embryo on dorsal surface of yolk, lb., 

 labrum ; wzoT., mandible ; ;«^.,' first maxilla; mx.j^ second maxilla;/.' — /.,^ the 

 three thoracic appendages (legs); coe., ccelomic sac of first abdominal segment 

 showing through the body wall ; //. {ap.^), pleuropodium (appendage of the first 

 abdominal segment) ; ?'., yolk ; tv/rV., cellular envelopes torn away from the ventral 

 face of the embryo ; cc. (ap."), cerci (appendages of the eleventh abdominal 

 segment). 



Fig. 7 (C). Surface view of shortened embryo on dorsal yolk, pc.,^ second 

 protocerebral lobe ; pc.,^ third protocerebral lobe ; dc, deutocerebrum ; Ic, trito- 

 cerebrum ; e., eye ; x., metastigmatic, or cenocytic invagination ; ap.,* fourth ab- 

 dominal appendage. Remaining letters as in Fig. 6 (F). 



Fig. 8 {//). Surface view of embryo turning the lower pole of the egg. sr., 

 inner indusium functioning as the serosa ; at/i., amnion reflected back over the 

 yolk and continuous with the membrane jr.; al., antenna; //., right pleuro- 

 podium ; zg^l., intraganglionic thickening. 



Fig. 9 (/). Surface view of embryo just after returning to the ventral face of 

 the egg. e., eye ; other letters as in Fig. 8 (//). 



Fig. 10 (A'). Surface view of advanced 9 embryo just before the secretion of 

 the larval cuticle, d.o., " dorsal organ " ; /.d., oviduct ; la., terminal ampulla of 

 oviduct ; op.'- {o/>.^), op.^ (cip-^), first and second pairs of gonapophyses (append- 

 ages of the 8th and 9th abdominal segments), cc. (iip.^^), cercus. 



