246 



PSYCHE. 



[ January — March 1SS5. 



such as we frcqueiitlv lliul niinorcil in 

 the embryonic growth of other animals. 

 This view seems to be supported by a 

 comparison of the modern and ancient 

 types of myriopoda. Tiie larval charac- 

 teristics of the young of living types of 

 myriopoda, marvelously analogous in 

 their main features to those of the larvae 

 of even the higher hexapoda, are confined 

 to the apodal nature of the abbreviated 

 abdomen, and more particularly to the 

 specialized development of appendages 

 on the segments directl}' following tiie 

 head. This specialized condition of the 

 anterior segments is, in a sense, analo- 

 gous to the structure of the thorax of tlie 

 hexapoila and is persistent throughout 

 life, — in the chilopoda in a marked 

 manner, in the other groups by tiie 

 isolation of these segments as bearing 

 but a single pair of legs. Now nothing 

 of this specialization appears in the 

 paleozoic types, of which of course we 

 know only the mature forms ; but the 

 segments following the head difler in no 

 point whatever from tiiose of the re- 

 mainder of the liiHiy in the character 

 and number of their appendages. In 

 one type, the archipolypoda, corres. 

 ponding in a measure to the living type 

 of diplopoda., two pairs of legs are borne 

 on every segment ; while in the other, 

 the p?-otosyngnatlia, corresponding in 

 a similar way to the chilopoda, a single 

 pair of legs is founil. If tiien we look 

 upon the specialization of the segments 

 (or tiie appendages of the segments) 

 immediateh- following the head in livins' 

 myriojiodan types as a secondary devel- 

 opment, or, we may say, as the initiatory 

 stage in an acquiring metamorphosis ; 



then we may perhaps consiiler the archi- 

 folypoda as the true prototx'pes of the 

 diplopoda and possibly also of the 

 fauropoda, and the protosy7igvatha as 

 the prototypes of the cJiilopoda. 



In tliis view, one principal distinction 

 between the modem diplopoda and 

 chilopoda is shown to have e-xisted 

 from paleozoic times, viz : that in one 

 group there are, over most of the body, 

 to each dorsal scute two ventral scutes, 

 each bearing a pair of legs; in the 

 other group a single ventral scute with 

 a single pair of legs ; and it becomes 

 interesting to inquire whether we can 

 disco\er any indication of tiie condition 

 of things from which this diversity of 

 structures arose, and what was the line 

 of development tiirough which it passed. 

 It will also help to determine the (jues 

 tion, whether the dorsal or the ventral 

 scutes of the diplopoda are to be looked 

 upon as the homologs of those of the chi- 

 lopoda ; or, in other words, wiietiier the 

 dorsal scutes of the diplopoda are com- 

 pound, or the ventral scutes of the same 

 are to be looked upon as subsegmeiits. 



It should be remarked at tiie outset 

 that what we know of the embryologv 

 of recent types shows that in the diplo- 

 poda two pairs of legs, in the chilopoda 

 one pair, arise from each original body- 

 somite beyond tiie front portion of the 

 body. This wouKl indicate that the 

 dorsal scutes of the two groups were 

 homologous and the ventral scutes of 

 tiie diplopoda shoidil be looked upon 

 as re]5resenting subsegmeiits. This, 

 however, is not the answer indicated 

 by the paleontological e\ idence, nor is 

 it what we slioidd expect from, among 



