I 



of the Oca of C\\t]um'iu:<. 207 



are not they a distinct aiuilo^ue of the nuclei of the vitelline 

 cells separated from the prutdplasin in C/it/ionius? As in 

 Philutlrinnus^ su also in Clithonuis^ and we may fairlv assume 

 in ( '/it lifer likewise, a jKtrtiou of the l)ri)ken-Uj) granules with the 



f)ortions of protonlasm surrouiulini; them work out of the vit(d- 

 ine spheres to their surface, whilst the (»ther part, with the 

 dentoplasm, becomes the entoderm. 



In C/it/iouiits^ as in P/tthx/romusj a total and, indeed, " un- 

 equal " segmentation takes place, such as we also meet with 

 elsewhere. For if we consider the amphi<;astrula of Parpura 

 (according to Selenka*), or the amjihigastrula ot' Pcfromi/zon 

 (according to Schultzet) and of Bomhinator (according to 

 Gotte|), or, lastly, the aniphigastrula o{ Fahricia or Trochns 

 (according to lliiekel §), and compare them with the amphi- 

 astrula of Chthonius (see fig. VII.) or Chelifer (according to 

 Metschnikoft' J, the close resemblance of all these structures 

 is at once percej)tible. 



Thus we Jind an agreement beticeen the amphigastrula of 

 Chthonius, or rather of the Chernetida;^ and the corresponding 

 emhri/onal structures not only of the Vermes and Arthropoda, 

 but also of the Mollusca and Vertehrata. 



In the aniphigastrula of Chthonius^ indeed, I have been un- 

 able to observe the primitive mouth ; possibly it is stopped by 

 a vitelline plug, as is the case in the amphigastrula of Bomhi- 

 nator according to Gotte. 



The eggs of the Chernetidje therefore furnish a new and 

 good contribution to the formation of the amphigastrula ; and 

 we must once more repeat Iliickel's words, " that the unequal 

 segmentation is tolerably widely diffused among the Arthro- 

 poda, but in most cases has not yet been accurately observed." 

 Moreover, by these results the investigations of Van Beneden 

 and BesselslI are again confirmed ; according to them, in the 

 different segmentations of the egg of the Arthropoda an ex- 

 tended series of transition forms occurs leading from one mode 

 of segmentation to the other. The segmentation of Chthonms, 

 although " unequal,^^ yet in many respects resembles the" super- 

 jicialJ' 



• Selenka, " Keimblatter bei Purpura,'' Niederl. Arch, fiir Zool. 1871, 

 Heft 2, pi. xvii. 



t M. Schultzp, ' Entwicklungsgeschichte von Petromyzon,' Haarlem, 

 18.06. pi. iv. tips. 5 & 7. 



I (Jotte, ' Keiinespe-schichte der Unite,' Leipzig, 1875, pi. ii. tig. 33. 

 § Hhcki'l, /. r. pi. vii. fig.^. 100 & 110. 



II Met-sclinikntl, " Knfw. dt>s Chelifer,'' I. c. pi. xxxviii. Hi,'. 0. 



51 E. van lii'noden pt Kmil Ik'ssfls, "Surla formation du lilastoderme 

 chez les Crustac4i>," Hull, ct Mt^m. de I'Acad. IJolg. iHfW, IHGO. 



