100 HYATT, 



gans ; but they are undoubtedly muscular, as is shown in 

 the figures referred to above. I found them, in all species 

 attached to the stomach above the origin of the fuuiculus, 

 and in every respect comparable with the other branches 

 of the gastric retractors. 



The oesophagal retractors, as regards their posterior 

 fibres, can hardly be separated from the gastric retractors 

 (PL 7, fig. 4, PL 8, fig. 2, PL 9, fig. 12, PL 10, fig. 1, 

 PL 12, fig, 1, PL 14, fig. 1, M') . These filaments attached 

 to the oesophagus, are, however, densely arranged-, and 

 whenever the three large muscles can be distinctly seen, 

 as in the younger stages of growth, or in a retracted adult 

 polypide, they invariably form part of the oasophagal 

 retractors. They perform for the cesophagal canal the 

 same office that the gastric retractors effect for the stomach ; 

 they hold that organ upright and unbent in its proper 

 place. The mode in which they act is especially remark- 

 able in Pectinatella, where they keep the posterior portion 

 of the oesophagus from being suddenly deflected during 

 the process of invagination, and thus protect the delicate 

 membranes immediately around the mouth and nerve- 

 mass from tbe strain to which they would otherwise be 

 subjected (PL 9, fig. 13). 



The filaments going to the lophophore diverge in fan- 

 shaped attachments, reaching abdominally more than half 

 way round the oesophagus, and extending more or less 

 dorsally according- to the generic rank of the individual, 

 and the greater or less degree of evagination displayed by 

 the evaginable tube. 



The brachial retractors do not distribute any filaments 

 to the alimentary canal in their passage from the ccenoeci- 

 um to the brachial collar of the polypide (PL 7, fig. 4, PL 

 8, fig. 2, PL 9, figs. 12, 13, PL 10, fig. 1, PL 12, fig. 1, 

 PL 14, fig. 1, M") differing from both of the other pairs 

 by having all the fibres attached to the endocyst in a uni- 

 form manner. 



Besides being more especially concerned in producing 

 the invagination of the polypide than any other muscles, 

 these retractors determine the motions of the crest. They 



