2:»2 KINGSLEY. [Vol. VIII. 



29 and 30, as they have either been treated of sufficiently in 

 previous papers or they are based upon conditions not described 

 in the present series. For the discussion of a large number of 

 the remaining points it becomes necessary first to review briefly 

 our knowledge of the homologies between the somites in the 

 principal groups of Arthropods. 



Until we have more evidence than we now possess of the 

 total disappearance of a somite from the anterior portion of 

 the body of any arthropod it will be necessary in making our 

 comparisons between the regions in the different groups to 

 proceed upon the assumption that the metamerically repeated 

 portions are, somite for somite, the same in the whole phylum, 

 and are to be compared throughout upon the serial basis, the 

 first being equivalent throughout, and so with the second, and 

 so on, the comparison ceasing only with the hinder region of 

 the body, where the budding zone occurs and behind which 

 is the terminal or caudal lobe. Upon no other basis can any 

 comparison be made. 



The great difficulty with this is in the recognition of the 

 metameres in the anterior end of the body for there we find a 

 tendency toward the obliteration of parts and the obsolescence 

 of those features by which the existence of the somite is made 

 most apparent. The nervous system seems, at present, to 

 afford us the most certain means of recognition of the somites 

 and upon this we must place the most dependence, since in 

 some cases the coelom of the somite may disappear, its meso- 

 derm becoming fused with that of its neighbors while the 

 appendages may totally fail to develop. In the Hexapods 

 various authors have expressed the idea that the so-called brain 

 was a compound structure, and of these the later writers — 

 Tichomiroff {teste Cholodkowsky) Patten ('88) and Cholod- 

 kowsky ('9i) represent it as composed of three neuromeres, and 

 Carriere (in Chalicoderma) has recognized still another in the 

 cephalic region. Of these the most anterior, the protocere- 

 brum, is apparently prestomial and hence is to be regarded as 

 homologous with the annelid cerebrum, and the descendant of 

 the "Scheitelplatte." All recent observers — Patten, Heider, 

 Wheeler, Graber, Carriere, Cholodkowsky r/. als. — have amply 



