198 Prof. J. von Kennel .o?i the 



their being allied to the Crustacea. Notwithstanding this, 

 however, with regard to the systematic position of these 

 animals I have arrived at quite a different conclusion, which 

 more nearly resembles tlie older ideas, and regards the Tardi- 

 grada as degenerate forms of higher Tracheates. Plate 

 declares that " the Bear-animalcules are tlie lowest of all the 

 air-breathing Arthropods with which we are at present 

 acquainted, and must be placed at the bottom of the Tra- 

 cheata, even below the Onychophora." Nevertheless, as may 

 well be imagined, he does not derive Peripatus from them, 

 but states that " they form an offshoot of the great Tracheate 

 stem, which, however, lies much nearer the root of the latter 

 than any other branch of that stock. They are the group 

 in which the transition from the Annelids to the air-breathing- 

 Arthropods is most clearly expressed and most distinctly 

 recognizable." 



To this opinion I am unable to assent. In the species of 

 Peripatus we have animals which furnish the best transition 

 between Annelids and Tracheates, and I have elsewhere * 

 explained at length the reasons why it is probable that forms 

 resembling Peripatus were the ancestors of the Myriapod- 

 like Tracheata, from which again the rest of the Tracheata 

 are descended. The bodily form, the organs of locomotion, 

 the commencing formation of head and jaws, the nervous 

 system, the eyes, the sexual organs, and the trachese of this 

 group of animals may without difficulty be brought into agree- 

 ment both with the conditions of the Annelids as also with 

 those of the Tracheates, and, in addition, we have the seg- 

 mental organs, which have been transmitted from the 

 Annelids. 



Conditions are different among the Tardigrada, which 

 present far less resemblance to the Annelids. In the first 

 place we are acquainted with no Annelids whose bodies con- 

 sist of so few segments as is the case among the Bear- 

 animalcules. It is true that such might have existed, or the 

 number of the segments might have been subsequently 

 reduced. But the Tardigrada do not possess even a trace of 

 true segmental organs, but are provided with Malpighian 

 vessels in their stead, and consequently in this respect they 

 must have receded far more from the Annelidan ancestors 

 than even the existing species of Peripatus ; they are in this 

 point much more Arthropods than the latter. The muscu- 



* Kennel, " Die Verwandtschaftsverhaltnisse der Arthropoden," 

 Schriften herausg. von der Naturforscher-Gesellschaft bei der Universitat 

 Dorpat, vi. 



