96 bulletin: museum of comparative zoology, 



between Callidiua and Eosphora, as described by Tessin. Nevertheless 

 it is possible that tlie slight titne variation in the cleavage of Eosphora 

 may have misled Zelinka as to the point which needed especial care. 

 In Asplanchua Heri'ickii and Asplanchna priodonta, in i\lelicerta and in 

 Callidiua, the large cell d^-^ divides first, followed immediately (in all 

 except Callidina, at least,) by the division of d*'^. In Eosphora, by a 

 slight relative delay of the cleavage in d'^-^ (a, Tessin), the cell d*'"^ (a", 

 Tessin) divides first. Zelinka states that he has observed with especial 

 care that the first cell (IV, Zelinka) given off in this quadrant takes 

 origin from d*-^ (I, Zelinka). This is doubtless true; the important 

 point, however, is the origin of the next cell formed. Though this also 

 is stated to arise from the ventral cell of the series (I, Zelinka), it 

 seems possible that Zelinka was thrown off his guard by the supposed 

 greater care necessary for determining the exact method of the preced- 

 ing cleavage, and that the statement with regard to this one is really a 

 mistake. The cell IV in Figure 23 (Taf. II.) of Zelinka's work might 

 be the same cell as V in his Figure 24, while the cells called III and IV 

 in Figure 24 might have arisen by the division of the previously exist- 

 ing cell III (= d^--). This would bring the conditions in Callidina 

 into agreement with those in Eosphora, Melicerta, and the two species 

 of Asplanchna. This is, of course, a mere suggestion, which indeed is 

 rendered rather improbable by the nuclear conditions in the cells under 

 discussion shown in Zelinka's Figure 24. There can, of course, be no 

 question about the manner of division in Asplanchna. Figure 16 (Plate 

 2) shows the spindles in rf* ^ and d'^-'^, and the accomplished division of 

 rf*-i into d^-^ and rf^-a jg shown in Figure 19 (Plate 3), while d*-^ still 

 contains a spindle. I have observed similar conditions in many other 

 specimens. 



In view of the essential similarity of the process in Eosphora, as 

 described by Tessin, to that in Melicerta, as described by Zelinka, and 

 in the two species of Asplanchna, as observed by me, and in view of the 

 fact that the cleavage of the quadrant in question {D) in these four 

 forms may be said to agree completely with the general plan of cleavage 

 as exhibited in the other three quadrants, — while in Callidina the con- 

 ditions in this quadrant are anomalous, — the following remark of 

 Zelinka ('91, p. 61) seems hardly justifiable: "Da, wie spater gezeigt 

 wird, auch Melicerta in der Entwicklung unserer vorliegenden Form 

 folgt, so muss der Vorgang bei Eosphora als eine bemerkenswerthe 

 Verschiedenheit aufgefasst werden." As above shown, the difference 

 between Eosphora and the other forms consists merely in a slight 



