ANNELIDA 349 



become possible, since the longitudinal stems in the two i 

 cases could be looked upon as corresponding to each other | 

 (whereby we even have in mind a former connection of the 5 

 permanent nephridia with the head kidney). At all events, ^ 

 the anatomy and development of the Annelid body permit 

 the establishment of the interpretation of the entire body ^ 

 as an individual. Just as in the consideration of the tape- \ 

 worm chain we were induced by the comparison with un- i 

 segmented forms to refer the entire chain to an unsegmented ; 

 individual/ and, on the other hand, to see in the proglottis, ] 

 not a complete individual, but only the abstricted hinder 

 portion of the body of the Cestode, in the same manner, | 

 and with much more reason, we adhere to the individualitv i 

 of the Annelid body. We can accordingly recognize in | 

 metameric segmentation only the regular repetition of certain I 

 groups of organs in the trunk at uniform intervals. i 

 In the question of the origin of the metameric segmenta- - /^ \ 

 tion we shall have to ascertain whether the synchronism J 

 of the terminal growth of the body and the appearance of ,' ; 

 metameric segmentation correspond to a palingenetic con- . ■ 

 dition. In other words, in the hypothetical ancestral form - { 

 were new segments successively added behind during in- ] 

 crease in length, so that forms with many segments arose ' i 

 from those with few by gradual increase in the number of ' J 

 segments ? The fact that the growth of the bo^iy in length " j 

 by the formation of new segments at the posterior end is ' l 

 typical in all Annelids and the forms tierived from them . j 

 (Arthropoda) is an argument in support of this theory. In j 

 that case w^ might perhaps be inclined to the opinion, as j, 

 stated by Hatschek, that in ancestral forms enlarging by 

 terminal growth the differentiation, originally progressing ^ '] 

 continuously, became intermittent, and thus reached the type ■ 

 of the metameric animal. But another view may also be 

 maintained, and, as it seems to us, with quite as much 

 justice — a view which is based upon the assumption that 

 at first an unsegmented, elongated ancestral form was pro- 

 duced by terminal growth, whereupon the entiue iSody be- -; 



^ There is a considerable difiference between this and the process of i 



strobilization. :; 



