1907.1 NATURAL SCIENCES OF I'illLADELI'IlI A. 357 



])ks, KIl'TION (»F rLATKS XX 1 1 I — X \ \1 1 1. 



All till' liiiurcs were drawn at tlic staj:^' IcN'cl witii tlic aid of tlio camera lucida; 

 plates XXIII, XX\ II and XWIII under Zi-i.ss Apoclironiatic Oijj. Itj nun., 

 Go. 1; plates X.\I\', .\.\V and XX\I with Obj. S mm., ( )e. 4. The figures of 

 the former plati's are therefore magnified (12 diameters; of the latter, 124 diam- 

 eters. In the process of reproduction the lifiures were reduci'd a little more 

 than half, so that as they appear on the plates they represent a maf^nilication of 

 about 30 diameters and (iO diameters respectively. All the drawings are of <'ggs 

 or embryos of Ftdgur carica, fixed, stained and mounted as described in the first 

 section of tliis paper. 



Plate XXIII. — Entire eggs; 1-cell to 24-cell stages. 



Fig. 1. — Unsegmented egg, sliowing first cleavage spindle and surroimding 

 cytoplasm. 



Fig. 2.^Two-cell stage, showing lajotropic turning of cytoplasm, nuchn and 

 spheres preparatory to the second cleavage. 



Fig. 3. — Four-cell stage; the positions of nuclei and spheres indicates that 

 the transverse furrow is here the second one. 



Fig. 4. — Eight-cell stage, showing first quartet of micromeres which have 

 turned in a dexiotropic direction ; in two of the macromeres are nuclear 

 spindles for the formation of tlie second cjuartct, which arises in a 

 la'otropic direction. 



Fig. 5. — Sixteen-cell stage. The first quartet ha.s divided heotropically, 

 giving rise to the "apical" cells centrally and the small " turret" cells 

 periplierally. The seeond quartet cells are dividing in two quadrants, 

 and the third quartet cells are arising dexiotropically from the micro- 

 meres. 



Fig. 6. — Twenty-four-cell stage, resulting from tlie completion of all tlie 

 divisions initiated in the preceding figure. 



Pl.vte XXIV. — Blastoderms during the earlier stages of cleavage. 



Fig. 7. — Same stage as sliowii in fig. 6, but magnified twice as much ; twenty 

 micromeres and four macromeres ; the separation of the ectoderm from 

 the macromeres is now complete. 



Fig. 8. — Forty-five-cell stage. Every cell of the preceding stage has dixided . 

 or is dividing, except the macromeres A, B and C. The '"apical" cells 

 have given rise to the "basals" of the arms of the cross; one .second 

 quartet cell in each cjuadrant has produced the "tip" cell (stippled) 

 of eacli arm: the tliird ciuartet cells are dividing hrotropically, and the 

 macromere D has produced the mesentoblast cell, -id. 



Fig. 9. — Fifty-five-cell stage. All divisions initiated in the preceding figure 

 are here' completed, and in addition the basal cells of the transverse 

 arms of the cross have divided. The mesentoblast (4d) has given rise 

 to six cells (two large and four small ones), and the macromeres A , B and 

 C have given off the other members of the fourth quartet, Aiz., 4.1, iB 

 and 4C. 



Fig. 10. — Fifty-six-cell stage. Similar to the preceding, but showing the 

 basal cellOf the anterior arm of the cross di\-ided and spindles in sonie 

 of the cells derivecl from tlie second quartet. The cross is shown in 

 heavy outline; there are three cells in each of the arms except the 

 posterior one. The centre of the cross is here, and elsewhere, marked 

 by a cross line, the "tip" cells of the arms, by stipples. 



Fig. 11. — Irregular Sl-cell stage; derived from prececUng stage by divi.sion 

 of the basal cell of the posterior arm, of eight cells of the third quartet, 

 of eight cells of the second quartet, and of eight turret cells. 



Fig. 12. — Eight v-five-cell stage: derived from the" preceding by the com- 

 pletion of iill divisions there indicated and by the subdivision of the 

 basal and middle cells in the transverse arms of the cross. 



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