240 ARTHUR WILLET. 



It is therefore a striking fact that the more primitive forms 

 have the indirect method of development. There is probably 

 a special significance in this seeming paradox, and in order to 

 get at the meaning of it, it is important to call to mind a 

 parallel case. The difference in the method of development 

 followed by Peripatus capensis and by Peripatus novse- 

 britannise is, allowing for the intra-uterine environment, 

 precisely the difference between direct and indirect develop- 

 ment. The egg of P. capensis ('5 mm.) is about five times as 

 larffe as the ess of P. novse-bri tannise, and there are not 

 wanting anatomical features which point to the more primitive 

 character of the latter species. 



Thus both in the Enteropneusta and in the Onychophora 

 the most primitive forms pass through an indirect development ; 

 and in both cases it is the indirect development which yields 

 information about the proximal relationships of the respective 

 groups; while the direct development apparently instructs us 

 in the matter of the primordial significance of the organisation 

 (cf. blastopore of P. capensis and body-cavities of B. kowa- 

 levskii). 



In their treatment of the development of Amphioxus, MM. 

 Delage and Herouard expose themselves to criticism at several 

 points. They have apparently overlooked the works of Van 

 der Stricht and Sobotta,i especially the latter, in which the 

 question of the polar bodies of Amphioxus is practically settled. 

 These authors found that the first polar body is extruded while 

 the egg is still inside the ovary, and a portion of the egg-mem- 

 brane is constricted off with the first polar body, so that the 

 latter comes to lie quite outside the membrane. When the 

 latter springs away from the egg at the time of fertilisation, 



1 Van der Stricht's paper, " La maturation et la fecondatiou de I'ceuf 

 d'Amphioxus lanceolatus" ('Arch, de Biol.,' xiv, 1895, p. 469), is 

 quoted in the bibliography at the end of the work, but Sobotta's latest important 

 paper on this subject is not quoted ; perhaps it is too recent. J. Sobotta, 

 " Die Reifung und Befruchtung des Eies von Amphioxus lanceolatus," 

 'Arch. f. mikr. Anat.,' vol. 1, 1897, p. 15. 



