542 A. A. W. HUBRECHT. 



region^ nor does his surface view iu fig. 5, pi. vi (1. c.), throw 

 any light on this question. I presume that he may have thus 

 concluded on a priori grounds, and feel inclined to suggest 

 that the region where sections 12 and. 13 were taken was 

 actually the anterior region of the embryonic shield. In 

 that case the crescent-shaped mesoblast might be interpreted 

 as mesoblast derived, from a hypoblastic protochordal plate 

 (not further mentioned, however, by van Benedeu), and its 

 presence before the appearance of any trace of the gastrula 

 ridge would be very well in harmony with facts which we have 

 observed in the shrew. However, it is only tentatively that I 

 advance this proposition, which only renewed researches of 

 very numerous early stages of the rabbit's blastocyst can 

 bring to a definite test. 



That the veteran leader in embryology, von Kolliker, retains 

 theoretical objections against any participation of the hypo- 

 blast towards the formation of mesoblast is well known, as 

 also that these views are all the more emphatically brought 

 forward in his later publication. He has experienced the 

 gratifying sensation that van Beneden, who in the publication 

 above cited (p. 142) most vehemently attacked Kolliker's 

 interpretations in terms which Kolliker resented, though he 

 referred to them very magnanimously {' Die Entwickelung 

 der Keimblatter des Kaninchens, Historische Vorbemerkungen,' 

 p. 5, Festschrift Wllrzburg, 1882), has since turned over an 

 entirely new leaf. In his latest, though as yet only prelimi- 

 nary communications on the rabbit and the bat (* Tageblatt 

 der Naturforschervers.,' Berlin, 1886, and 'Anat. Anzeiger, 

 iii, 1887) van Beneden not only wholly accepts Kolliker's 

 views, but draws very full and far-going conclusions from 

 them. As such we may consider his theory of the gastrulation 

 of the Mammalia, their blastophore and lecithophore. 



If we consider the plate by which Kolliker's essay just 

 cited is illustrated, we find in the surface views a crescentic 

 " vorderer Randbogen." This seems to correspond with van 

 Beneden's crescentic mesoblast above alluded to. Iu the 

 text (p. 9) Kolliker compares these stages with those of van 



