124 
darkened. With the face and eyes protected by a screen, the observer 
may work in comfort for hours. 
The eggs from which all but the innermost jelly had been re- 
moved, were placed some time before the appearance of the dorsal 
lip, in a ZIEGLER’s compressorium (large form), and slightly com- 
pressed. Thus normally placed, they develop normally if a proper 
current be maintained, and they are not overheated. The thickness 
of the two under glasses in the ZIEGLER’s compressorium might seem 
to be a serious disadvantage, but with a 3/, inch objective, and a 
Zeiss 2 ocular, the change of shape and position in the individual 
cells may successfully be studied. The cells are not however equally 
distinct round the entire periphery, and the compressorium must be 
turned until the quarter of the egg which it is desired to study, oc- 
cupies the proper position with respect to the light. Or it is usually 
better to include a number of eggs in the compressorium, and simply 
select those which occupy the desired positions. 
The observations upon the cell movements were carried on with 
the help of a micrometer eye-piece, and the egg used was again that 
of Chorophilus feriarum Barrp. Out of seven sets of observ- 
ations made during March, two were failures owing to the fact that 
the eggs developed too slowly, and eventually became abnormal. Five 
were successful, the development progressing normally with formation 
of neurulas. The observations showed that the same processes as de- 
scribed for the inverted eggs occur in the normally placed egg: the 
process of “delamination” occurs; blastopore is outlined in same way; 
ectoderm cells roll over the dorsal and ventral lips; and yolk cells 
disappear beneath the dorsal and ventral lips during the extension 
of the ectoderm over the yolk, the rate of approximation between 
yolk cells and the lip being about the same for the dorsal and ventral 
regions. 
Of the five successful sets of observations, I select one for de- 
scription. Eggs were laid in the laboratory by a copulating pair, 
March 12 about 8 P.M. Nine eggs in an advanced stage of segmen- 
tation were put in the compressorium March 13, 11 A.M. and slightly 
compressed. They were exposed to lamp light with bulls-eye lens all 
day. Continuous observation began at 6.30 P.M. Excellent results 
here as in some other cases were obtained through the long exposure 
to light. Numerous yolk cells acquired a slight tinge of brown, rend- 
ering cells outlines more distinct. In many yolk cells, central pigmented 
spots due to accumulation of pigment round the nucleus, appeared. Also 
