96 ENTOPROCTA. 



The structure of these excretory canals has been repeatedly investigated in 

 the adult of Loxosoma, Pedicellina, and Asc(ypoda7'ia, a certain importance being 

 attributed to these forms in connection with the significance of this organ as the 

 head-kidney (protonejihridium, Hatschek). The results of these investigations 

 must not as yet be regarded as conclusive. "While Harmer, Foettinger, and 

 Hatschek regard the cells of this organ as perforate, and its lumen thus as 

 being intracellular, Ehlers, and more recently Prouho (No. 9), do not agree 

 with this view. According to the latter authors, the lumen of the canal lies 

 between the cells. According to Ehlers, the canal, ends blindly internally, 

 but does not, as Harmer stated, terminate with a flame-cell. The most recent 

 investigator of this subject (Prouho) even throws doubt on the blind termina- 

 tion of the internal end. According to Foettinger and Ehlers, the two 

 canals unite to form a common unpaired duct opening by a single aperture. 



Metamorpliosis. 



According to the statements of the older investigators (P. J. van 

 Beneden and others), the fixation of the Pedicellina larva seemed 

 to take place by means of the ciliated disc. This organ was then 

 said to pass over into the pedal gland of the Loxosoma stage. It 

 was therefore usually called, even in the larva, the "cement-gland, or 

 sucker," or" received some other similar appellation. Metamorphosis 

 would then simply have consisted in the growing out of the apical 

 part of the larva as the peduncle, while the organisation of the adult 

 would be attained by the budding out of tentacles in the vestibule. 

 On the other hand, the more recent researches of Barrois (No. 1), 

 which were confirmed by Harmer (No. 5), have revealed the sur- 

 prising fact that the fixation of the larva takes place, as in the 

 Ectoprocta, at the oral side, by means of the edge of the vestibule. 

 During fixation the larva is in its most retracted condition (Fig. 46 A), 

 even the cell-row of the ciliated ring being Avithdrawn into the 

 vestibule. The aperture of the latter is very much narrowed, and 

 soon closes completely, and its marginal cells fuse (Fig. 46 B). In 

 this way the vestibule becomes a sac closed on all sides. 



In the course of further metamorphosis, the body of the larva 

 changes in shape. The lower part narrows somewhat to form the 

 future peduncle (Fig. 46 B and (7), while the upper part swells out 

 into the head, this swelling being at first more marked posteriorly. 

 The body in this way becomes almost pipe-shaped (Fig. 46 G). At 

 the same time the alimentary canal, together with the vestibule, 

 changes its position, its posterior portion shifting upwards. The 

 stomach, the principal axis of which originally lay horizontally, has 

 now assumed a more oblique position, which finally passes into a 

 perpendicular position. The oesophagus then lies below, while the 

 hind-gut with the anal aperture (a) lies above. These two parts 



