84 GARDINER. [Vol. XV. 



within it the centrosome. Also, a few words are necessary on 

 the methods employed. Although in the egg-bearing animal, 

 and without injury to the animal, it is easy to determine 

 whether the ova are immature, about ripe, or whether the 

 amphiaster of the first segmentation cleavage has already been 

 formed, nothing further can be decided except by sections. 

 That is, no information whatsoever in regard to the formation 

 of the polar bodies or fertilization of the ovum can be obtained 

 by examination of the ova within the living parent. It was, 

 therefore, found most convenient and time-saving to kill large 

 numbers of individuals which examination with a hand lens 

 showed to contain large ova. Several of these were imbedded 

 in one block and sectioned without attempting to orient the 

 position of the ova. It was found that all the ova in one 

 animal were in very nearly the same stage of development, 

 but that the position of the axes of different ova differed ; 

 hence a section through the long axis of one ovum might cut 

 the ova next to it at a very different angle. 



In this manner many hundred animals were sectioned, each 

 containing on an average half a dozen to a dozen or more eggs. 

 The size of the ova allowed from six to eight sections through 

 each, and as the whole worm was sectioned, the successive sec- 

 tions of any one ovum might be quite a distance apart. This 

 involved the use of a low power in order to be sure that the sec- 

 tion under inspection was the next in the series, and also every 

 section had to be carefully examined with the highest power 

 before the exact stage of development could be determined. 

 Hence, the amount of labor necessary to obtain anything like 

 a continuous history of the changes which occur in the ova has 

 been very great. 



It was found that by far the most frequent stages were 

 either the nucleus intact, or the complete amphiaster of the first 

 segmentation cleavage fully formed, showing that the changes 

 between these two stages took place with great rapidity. 

 There are, as will be pointed out later on, several short gaps 

 in the chain of events between these two stages, but to fill 

 these an indefinite amount of section cutting might be required, 

 and the prospects of success were not sufficient to encourage 



