January — March 1885.] 



PSYCHE. 



245 



lire and development of the different 

 tjroups. 



In the early life of the pauropoda and 

 of the diplopoda we have what may be 

 fairlv considered a true larval form, in 

 which, for a brief period after leaving 



THE GEOLOGICAL HISTORY OF MYRIOPODS AND ARACHNIDS. 



BY SAMUEL HUBBARD SCUDDER, CAMBRIDGE. MASS. 

 [Eiglitli annual address of the retiring president of tlic Cambridge Entomological Club.] 



As the only subject of a general natiu'e tcresting in the m\riopoda than in either 

 to which I have given recent attention I the arachnida or the hexapoda. That 

 venture to invite you to review with me these relations are equally puzzling will 

 the geological history, first of myriopods appear from a brief review of the struct- 

 and then of arachnids. Unusual atten- 

 tion has recently been paid to these ani- 

 mals, on account of the discovery of 

 their remains in formations much ear- 

 lier than those from which they had for 

 a long time been known, and the rela- 

 tion of these discoveries to our previous the egg, the Iiodv, much shorter than in 

 knowledge will be best brought out bv after life, is provided with three pairs of 

 such a review, and it will, to a certain legs borne upon the anterior segments 

 extent.be timely. of the body. These segments are never 



Our knowledge of the moiphology, more full}- provided with legs, though 

 systematic position and extent of the most of the segments posterior to them, 

 myriupoda has been greatly increased both those which exist dm'ing this larval 

 within a recent period. The discovery period and those which originate subse- 

 of the minute Paiiropiis Iiy Lubbock, quently, bear two pairs. In the chilo- 

 anil the stuth' of this and allied forms by poda, on the other hand, although the 

 R\der and others, have led to the estah- appendages of the anterior segments de- 

 lishment of the pauropoda as a type of velop earlier than those behind them, 

 living myriopods oi equal taxonomic there is no true larval condition, or 

 \alue to the two groups of chilopoda perhaps one may say a larval condition 

 and d iplopoda which had long been is permanent, in that the same anterior 

 looketl upon as the only divisions of the legs become early and permanently 

 group. Modern investigations into the developed as organs subsidiary to man- 

 structure of the anomalous Peripat7(s ducation, while the segments of the 

 have extended our ideas concerning tile hinder part of the body develop onl\- a 

 types allied to the myriopoda ; while the single pair of legs. 



strange forms revealed by recent re- The larval condition and resultant 



searches in the carboniferous and devon- more or less highly developed metamor- 



ian faunas have compelled us to recog- phosis of the higher hexapoda have been 



nize a wider range in its structure and looked upon by many as a secondary 



a multiplication of its primary groups. after-development, and one which there- 



The relations of ancient to modern forms fore in no sense gives any clue to the 



of life prove far more important and in- historical ilevelopment of the group. 



