The American journal of anatomy . heir membranes, werefree to adjust themselves to gravity, as care was taken to preventthem from becoming attached to the mirrors surface. Conse-quently, it was assumed that the primary axis would take the per-pendicular. Apparently, such was not always the case, to judgefrom one or two instances, which have been discussed above. The discrepancies apparent in the figures between the marks on dif-ferent days, especially in the upper hemisphere, are the results of differ- DEVELOPMENT OF SPELERPES BILINEATUS 227 ences in judgment or of observation as to whether a
The American journal of anatomy . heir membranes, werefree to adjust themselves to gravity, as care was taken to preventthem from becoming attached to the mirrors surface. Conse-quently, it was assumed that the primary axis would take the per-pendicular. Apparently, such was not always the case, to judgefrom one or two instances, which have been discussed above. The discrepancies apparent in the figures between the marks on dif-ferent days, especially in the upper hemisphere, are the results of differ- DEVELOPMENT OF SPELERPES BILINEATUS 227 ences in judgment or of observation as to whether a given mark shouldbe recorded or not. If a mark was faint it might be recorded one dayand the next considered too faint to record. Figs. 56^3 represent the changes observed in an egg, whoselower hemisphere was studied in the way just described. Theupper hemisphere is shown in the upper row, the lower in the lowerrow. The movements of the marks are so clearly shown that adetailed description is not necessary. It should, however, be. Figs. 56-63 noted that in the region dorsal to the blastopore, the marks aretoo far above it to be drawn into it. In figs. 62-63 the stainhas faded so badly that it is no longer of much value. The interpretation of the movements described above is notdifficult. As already stated, Nile blue sulphate stains the yolkgranules. Hence the extension of the marks denotes cell divisionfollowed by an active migration of some of the parts towards theblastopore. The region of this cellular activity lies in a bandabout the equator. The cell activity may begin above the dor-sal lip slightly in advance of that on the opposite side of the egg,since it has been noted sometimes, that marks lying above thedorsal lip begin to extend somewhat before those of the oppositeside. Aided by this start, and the nearness of the blastopore, 228 HUBERT DANA GOODALE which remains noarly stationary, the cells above the lip reach itfirst, then the cells of the lateral parts of the equ
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectanatomy, bookyear1901
