Classification of the Arthrojjoda. 367 



into consideration that the breathing by air-spaces may have 

 been developed in different ways and at different times in the 

 terrestrial forms, and that consequently no primarily decisive 

 morpholog-ical value is to be ascribed even to the possession 

 of trachea?." Here again Prof. Claus is simply repeating a 

 statement made four years ago by me in the following words; 

 his " hitherto " is totally without justification, excepting so 

 far as it applies to his own systematic treatises. 



In " Limulus an Arachnid " I say, " Whatever may be 

 tlie conclusion arrived at in the future in reference to the 

 affinities of the Hexapoda and Myriapoda, the result of the 

 recognition of the intimate relationship of Scorpio and Limu- 

 lus must be, I think, to break up the artificial group of Arthro- 

 poda Tracheata by the separation of the Scorpions, Spiders, 

 and Mites from any special connexion with it." And again, 

 in another passage of the same essay, my words run : " It 

 seems to be in the highest degree probable that there is no 

 such a group to be recognized as the Tracheata. Trachea? 

 have probably developed independently in Peripatus, the 

 Insecta, and again in Arachnida." 



IV. Proceeding to formulate the conclusions which he has 

 taken bodily from me as to the probable genealogy of the 

 chief groups of the Arthropoda, Prof. Claus states that the 

 stem of the Crustacea and that of the Arachnida are united 

 at the base, whilst the Insecta Hexapoda and Myriapoda 

 form a third series, " for the derivation of which the remark- 

 able Annelid-like Onychophora (Peripatus) appear to be so 

 significant." 



This is a simple and direct description in words of the 

 genealogical tree of the Arthropoda given at the end of my 

 article " Limnlus an Arachnid," with this difference, that 

 whilst I have represented the Crustacea and the Arachnida 

 as two main stems with a common base, and Peripatus as a 

 third and independent stem, I have indicated a hesitation to 

 decide on referring the Insecta Hexapoda and Myriapoda to 

 the stem of Peripatus absolutely, and have considered the 

 possibility of their derivation from either the Arthrostracous 

 Crustacea or the tracheate Arachnida. 



In the text of the essay I have, however, weighed the 

 three possibilities suggested, and hav^e given the reasons for 

 considering the Insecta Hexapoda and Myriapoda to be derived 

 from Peripatus. The most important of these reasons is 

 pointed out by me to be dependent on the character of the 

 antennae of the Crustacea on the one hand, and of those of 

 Peripatus and of the Insecta Hexapoda and Myriapoda on the 

 other hand — the latter being apparently identical with the 



25* 



