of the Ova o/" Chthonius. 207 



are not they a distinct analogue of the nuclei of the vitelline 

 cells separated from the protoplasm in Chtkonius? As in 

 Philodromiis, so also in Chthonius, and we may fairly assume 

 in Chelifer likewise, a portion of the broken -up granules with the 

 portions of protoplasm surrounding them work out of the vitel- 

 line spheres to their surface, whilst the other part, with the 

 deutoplasm, becomes the entoderm. 



In Chthonius, as in PhilodromuSj a total and, indeed, " un- 

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

 elsewhere. For if we consider the amphigastrula of Purpura 

 (according to Selenka*), or the amphigastrula oi Petromyzon 

 (according to Schultzef) and of Bombinator (according to 

 (lOtte:):), or, lastly, the amphigastrula of Fabricia or Trochus 

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

 gastrula of Chtkonius (see fig. VII.) or Chelifer (according to 

 Metschnikoffli), the close resemblance of all these structures 

 is at once perceptible. 



Thus loe find an agreement between the amjpiigastrula of 

 Chthonius, or rather of the Chernetidce, and the corresponding 

 embryonal structures not only of the Vermes and Arthropoda, 

 but also of the Mollusca and Vertebrata. 



In the amphigastrula 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 Bombi- 

 nator according to Gotte. 



The eggs of the Chernetidee. therefore furnish a new and 

 good contribution to the formation of the amphigastrula ; and 

 we must once more repeat Hackel'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 tlie investigations of Van Beneden 

 and Bessels^ are again confirmed; according to them, in the 

 different segmentations of the e,^g of the x4.rthropoda an ex- 

 tended series of transition forms occurs leading from one mode 

 of segmentation to the other. The segmentation of Q\\i\iomus,y 

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

 ficiaiy 



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

 Heft 2, pi. xvii. 



t M. Schultze, ' Entwicklungsgeschichte von Petromyzon^ Haarlem, 

 1856, pi. iv. figs. 5 & 7. 



X Gotte, ' Keimesgeschichte der Unke,' Leipzig, 1876, pi. ii. fig. 33. 



§ Hackel, /. c. pi. vii. figs. 100 & 110. 



II Metschnikoff, " Entw. des Chelifer^'' I. c. pi. xxxviii. fig. 9. 



% E. van Beneden et Emil Bessels, " Surla formation du Blastoderme 

 chez les Crustacea," Bull, et Mem. de 1' Acad. Belg. 1868, 1869. 



