SEGMENTATION OF THE HEAD OF DIPLOPODA. 615 



improbable that more than one pair of appendages are con- 

 cerned in the formation of the guathochilarium. 



Stage B (fig. 2). 



This is the stage which immediately precedes the breaking 

 and final casting off of the egg-sheU. In an external view of 

 it there can be seen : 



(1) The three-lobed archicerebrum. 



(2) The antennary ganglia, to which the tritocerebral rudi- 

 ments are now joined, and which still lie behind the mouth. 



(3) The ganglia of the mandibles. 



(4) The ganglia of the maxillulte, much reduced in compara- 

 tive size. 



(5) The ganglia of the maxillary segment. 



(6) The ganglia of a post-maxillary segment which is 

 without appendages. 



(7) The ganglia of the three segments bearing rudi- 

 mentary legs. 



There are also to be observed the mouth and the clypeus, 

 as well as a pair of appendages for each pair of ganglia, 

 excepting that in the post-maxillary segment. 



In each of the three lobes of the archicerebrum and in 

 every other ganglion there can now be seen a distinct 

 depression, a little pit in fact, the opening of which lies in 

 about the middle of the ventral surface of the ganglion. 

 Heathcote (1888) mentions these depressions as occurring in 

 the ganglia of the embryonic Jul us, but states that they 

 do not appear until the ganglia have left the ectoderm. He 

 also says that he does not consider them to have anything to 

 do with the " cerebral grooves." These " cerebral grooves " 

 are similar cavities which he found in the ganglia of the 

 embryonic brain. 



In my specimens I can find no difference between the 

 depressions in the ganglia forming the archicerebrum and 

 those in the ganglia of the cords ; and further, these depres- 

 sions seem to me to appear before the ganglia have com- 



