The Ohio 'ihC^aturalist, 



PUBLISHED BY 



The Biological Club of the Ohio Slate Uni'versity. 

 Volume VIII. FEBRUARY. 1908. No. 4. 



TABLE OF CONTENTS 



Landacre— The Epi-brancliial placodes of Ameiurus 251 



SCHAFFNER — Oil the Origin of Polar Conjugation in the Aiigiospenns 2P5 



HiNK — Some Observations Ci neerning the EfTects of Freezing on Insect Larvae 258 



Hammond— The Embryology of Oxalis corniculata 261 



Sterki — Some Notes on Pnilomycns 265 



Hammond— McCray— Meetings of the Biological Club 267 



J. C. H— Book Review 269 



THE EPI-BRANCHIAL PLACODES OF AMEIURUS.* 



F. L. Landacre. 



The study of the epi-branchial placodes of Ameiurus was 

 taken up with the object of ascertaining to what extent the}^ 

 enter into the composition of the cranial nerves in this group 

 of Teleosts. 



The catfishes with their enormously hypertrophied system of 

 gustatory nerves ought to have these placodes correspondingly 

 prominent during embryonic development if they are concerned 

 in the origin of the communis portions of the cranial ganglia. 



Ameiurus has proven to be an unusually favorable type and 

 a study of the development of its epi-branchial placodes suggests 

 the idea that possibly the extremely divergent accounts given in 

 the literature of these structures may be due to the choice of 

 unfavorable types for study. 



The extent to which communis fibres enter into the composi- 

 tion of the cranial nerves varies greatly even among the teleosts. 

 There is probably a corresponding variation in the distinctness 

 with which the placodes may be traced in the early development 

 of those types in which the system is reduced. At any rate they 

 are far more prominent and easily followed in Ameiurus than 

 they seem to be in any other form described. 



Aside from working out the details of their origin the follow- 

 ing queries have been kept more or less constantly in mind: 



(1) Do the cells derived wholly or in part from the placodes 

 really become the communis ganglia of the adult? 



(2) Are the placodal portions of the cranial gangHa pure— 

 i. e., are the communis ganglia derived exclusively from the 



* Read at the 1907 meeting of the Ohio Academy of Science. 



