A NEW TYPE OF BRYOZOAN GIZZARD, WITH 

 REMARKS ON THE GENUS BUSKIA. 



RAYMOND C. OSBURN and RUTH M. VETH 

 Department of Zoology and Entomology, Ohio State University 



A certain few of the Ctenostome Bryozoa have long been 

 known to possess a gizzard or grinding organ at the cardiac 

 end of the stomach, though such information may be sought 

 for in vain in nearly all text books dealing with the group. 



This structure is best known in the genus Bowerbankia 

 Farre, owing to the work of Hincks (1880, text figure on p. xxiii 

 and discussion on pp. xxiv-xxvii), and especially to the excellent 

 histological description by Calvet (1900, p. 227-230, 232- 

 234, PI. VI, Fig. 13 and PI. VII, Fig. 4). 



Davenport (1891, p. 63) incorrectly homologizes the gizzard 

 with the lower end of the chilostome oesophagus. Calvet (1900, 

 p. 233) is undoubtedly correct in stating that it is the cardiac 

 end of the stomach which is thus modified. 



The genera Amathia Lamouroux, Vesicularia Thompson and 

 Avenella Daly ell also possess a gizzard similar to that of Bower- 

 bankia. All of these genera belong to the family Vesiculariidae. 



In the foregoing genera the gizzard has the appearance of a 

 rounded distension of the cardiac end of the stomach, or, to 

 quote Calvet (p. 228), "la forme d'une sphere tronquee aux 

 deux poles." The epithelial lining of the gizzard consists of 

 enlarged and elongated cells which are easily visible under the 

 ordinary low power of the microscope. The walls of these cells 

 at their inner free ends are heavily chitinized, so that each cell 

 thus presents a separate pointed chitinous tooth for the tritura- 

 tion of the food, (see Fig. 8). The bryozoan gizzard as thus 

 described is unique in its armature. 



A strong layer of circular muscles completes the grinding 

 apparatus, which operates by rhythmic contraction and relax- 

 ation. Hincks (1880, p. xxvii) states that he has seen the food, 

 after passing through the gizzard, driven back into it by a 

 retrostaltic movement of the stomach and again submitted to 

 its action. 



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