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The Morphology of the Swim-bladder in Teleosts. 



(Preliminary statement.) 



By Henry C. Tracv, Ph.D., Northwestern University Medical School, 



Chicago, U.S.A. 



With 10 Figures. 



The morphology of the swim-bladder in Teleosts is probably less 

 thoroughly understood than that of almost any other organ in the verte- 

 brates. This appears to be due, partly to the confusing multiplicity 

 of its anatomical relations in different species, but more especially to 

 our ignorance of its ontogeny. A cause of the comparative neglect of 

 this subject is doubtless to be found in the fact that the swim-bladder 

 develops chiefly during the larval and post-larval stages, and the de- 

 velopment of fishes during this part of their life history has received 

 little attention. Many investigators, indeed, have considered certain 

 aspects of the embryology of the swim-bladder, but their interest has 

 more often been concerned with the relation of this organ to the lung 

 of higher vertebrates than with the study of the morphology of the 

 swim-bladder for its own sake. Since von Baer (1834—1837) there 

 has been, so far as I am aware, no systematic investigation of the 

 comparative embryology of the swim -bladder in different groups of 

 Teleosts, except the work of Moser (1904), who studied the develop- 

 ment of the organ in certain of the species which retain the pneumatic 

 duct throughout life (Physostomi). 



The following paper is a brief, preliminary statement of the re- 

 sults of an anatomical and embryological study of the swim - bladder, 

 particularly in certain of those fishes in which the pneumatic duct 

 atrophies during development (Physoclisti). Certain facts have been 

 established, and upon these is based a theory of the morphology of 

 the swim-bladder; also, certain questions have been raised which may 

 be the subject of further investigation. The development of the swim- 

 bladder in the following species has been studied: anchovy (Stolephorus 

 mitchilli), Fundulus heteroclitus, Menidia menidia notata, toadfish (Opsanus 

 tau), pipefish (Siphostoma fuscum), cunner (Tautogolabrus adspersus), 

 and tautog (Tautoga onitis) ; also, isolated stages of other species, the 



