SEGMENTATION OF THE HEAD OF DIPLOPODA. 611 



Scolopendra; describes the primitive brain as consisting 

 of three lobes on either side. In his drawing, which, like 

 mine, is somewhat diagrammatic, the lobes lie more in series 

 than do those shown here (PI. 37, fig. 1). Nevertheless, there 

 is a great similarity between the two brains. 



It seems that we have in the Archispirostreptus embryo 

 an archicerebrum, in Professor Lankester's (1881) sense of 

 the word (Heymons uses the words " archicerebrum " and 

 "syncerebrum" with a different meaning), and one cannot help 

 being reminded of the fact that in the Cheetopod brain, also 

 an archicerebrum, there are three areas (Pruvot, 1885, and 

 Racovitza, 1896). 



The first post-oral ganglion, which is here very small, con- 

 sisting of a just visible expansion of the thickening, is that 

 belonging to the first post-oral segment which bears the 

 antenna. I can find no trace of a pre-antennary segment in 

 this embiyo. 



The segment which lies immediately behind the imperfectly 

 closed nerve-ring is apparently the tritocerebral segment 

 (intercalary segment of Heymons and others). It has no 

 appendages, but shows distinct rudiments of a pair of ganglia, 

 and is definitely cut off by grooves from the antennary 

 segment in front and the mandibular segment behind. 



The "intersegmental furrows" (Heymons) seem here to 

 appear first in the median region of the blastoderm, while in 

 Scolopendra, according to Heymons (1901) they make 

 their first appearance laterally. 



The rudimentary nervous system is here extremely small and 

 difficult to make out. From the deep way in which it stains 

 with Delafield's hgematoxylin, I believe it to be as yet merely 

 a thickening of the ectoderm. 



Behind the mouth, a very little way in front of the first 

 " intersegmental furrow," there is a very slight expansion of 

 the thickening on both sides of the nerve-ring. This expansion 

 I take to be the first indication of the antennary ganglion. 

 The ring is not completely closed, but the two cords lie very 

 near each other behind the imperfect closure. These cords 



