No. 2.] STOLONIZATION IN AUTOLYTUS VARIANS. 311 



les segments nouveaux, s'il renfermait les tissus embryonnaires 

 en voie active d'accroissement, la zone de proliferation des 

 nouveaux segments, et par consequent des nouveaux bourgeons, 

 serait irremediablement entrainee avec lui. D'autre part, nous 

 verrons plus loin qu'il existe des zoonites formateurs tres eloignes 

 du pygidium et absolument independants de ce dernier." In 

 describing the stolon of Autolytus edwarsi he makes the same 

 observation : " II est inutile d'insister ici sur I'accroissement 

 du corps, c'est-a-dire sur la formation de nouveaux anneaux, 

 qui est toujours identique a ce qu'elle est partout. 



" C'est le Zoonite formateiir qui en se multipliant, produit de 

 nouveaux anneaux et fait s'accroitre le corps d'avant en arriere. 

 Les caracteres de I'individu et de I'espece restent identiques 

 pendant cette pe'riode d'accroissement qui s'etend de I'individu 

 jeune a I'individu adulte possedant 50 a 60 segments." 



My observations in sections of Autolytus varians do not 

 accord with this view. In young stolons corresponding in age 

 to stolon I, PI. XIII, Fig. 6, sections of the posterior part of 

 the stolon plainly indicate the absence of any embryonic tissue 

 anterior to the pre-anal segment (PI. XIV, Fig. 23), and hence 

 the absence of a region in which the formation of new seg- 

 ments could take place. The pre-anal segment in this stolon 

 furthermore presents the appearance of having quite recently 

 been separated from the anal segment, this accounting for the 

 embryonic tissue seen in this segment, and also indicating 

 the manner in which new segments make their appearance. 

 In stolons with a greater number of segments than the one 

 just referred to, the pre-anal and several segments anterior to 

 it do contain embryonic tissues very little more advanced in 

 the more anterior segments than those of the anal segment 

 itself ; and it is in such segments that we found traces of ex- 

 ternal segmentation that would indicate the formation of new 

 segments in a region anterior to the anal segment. In older 

 stolons, however, where the formation of new segments is no 

 longer as rapid, this embryonic tissue (PI. XIV, Fig. 26) is 

 again confined to the anal segment and new segments must 

 hence be derived from this region. Since the anal segments 

 contribute the very first segments toward the elongation of the 



