98 HYATT, 



entirely retracted, but their distinctness is produced wholly 

 by the extreme tension of the fibres. Under ordinary cir- 

 cumstances, the anterior attachments are not separable 

 from each other and often single bundles seem to have dis- 

 tinct anterior bases. This is especially the case with the 

 anterior branch of the gastric retractors in Pectinatella 

 (PL 9, tig. 13, PL 10, fig. 1, M.) because of the great size 

 and peculiar deflection of the alimentary canal from the di- 

 rect line of action of the retractors. 



Although this differentiation of the anterior branch of 

 the gastric retractors may be occasionally seen in Fred- 

 ericella, Plumatella and Cristatella it is not habitual, since 

 the stomachs of the polypides in these genera, usually lie 

 in the same, or nearly in the same plane with the retrac- 

 tors. When, however, complete iuvagination takes place 

 and the stomach of the polypide shoots past the bases of 

 the retractors, the anterior branch separates from the 

 other retractors and assumes precisely the same aspect in 

 these genera that it habitually has in Pectinatella. 



The freedom of motion manifested by every minute 

 bundle of fibres is the one great peculiarity of the larger 

 bands. Each bundle has the faculty of acting separately 

 in the gastric retractors, and though this independence is 

 less noticeable in the other retractors, because of the clos- 

 er association of the bundles, it is still appreciable. 



In Plumatella diffusa a very singular conjunction of 

 the retractors sometimes takes place. They are brought 

 together on the abdominal side of the stomach, and held 

 there as if bound by a narrow muscular band. The poly- 

 pide when this conjunction occurs, is bent over towards the 

 abdominal side, and the stomach displaced by the com- 

 bined muscles. 



Dumortier and Van Beneden* recognized the existence 

 of isolated fibres attached to the endocyst at the base of 

 the arms, and Prof. Allmanf showed them to be of equal 

 size and value with the internal branches (cesophagal re- 



* DUMORTIER and VAN BENEDKN. Op. cit. t. 16, p. 86. 

 f ALLMAN. Op. cit. 



