No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 27 



in the same ^g^. In the first case the embryo itself was in 

 every way normal, and the first indusium of the normal size 

 and shape, and in the usual position. The second, somewhat 

 smaller, though regularly circular organ, was situated in front 

 of the first and a little to the right of the median line. The 

 distance between the two organs was about double the distance 

 between the first organ and the head of the embryo. The 

 outlines of the second or more anterior organ were less definite 

 than those of the first. The amnion and serosa had formed 

 over the embryo, but neither of the indusia showed as yet any 

 tendency to form envelopes. Whether these two organs were 

 derived from the division of one original praeoral cluster of cells, 

 or were originally established as two separate centres on the 

 blastoderm, I am unable to decide. The latter method would 

 seem to be the more probable. 



The other case is somewhat singular. The first indusium 

 was normal in size and position, but irregularly heptagonal 

 in outline. The second, situated a short distance to the 

 side of the right procephalic lobe, was not more than a third 

 the size of the first organ and quite regularly quadrangular. 

 The embryo itself was normal and covered with the amnion 

 and serosa. The envelopes had also formed over the two 

 organs, which in this case also probably originated from two 

 discrete centres in the blastoderm. The smaller organ had 

 probably never been attached to the head of the embryo. 



5. TJie Revolution of the Embryo 



During the first warm days of spring the Xiphidiiim embryo 

 resumes its development. This is characterized for some time 

 by a growth of the germ-band in breadth and length and a 

 lengthening of the appendages. The body of the embryo, 

 which in Stages F and G was much narrower than the ^gg 

 now becomes almost as broad so that its pleural edges embrace 

 the yolk. This increase in size brings the head somewhat 

 nearer the lower pole, and there soon sets in a decided move- 

 ment of the whole body in this direction. When the head has 

 almost reached the lower pole, the amnion covering the face 



