On the Formation of the Germinal 

 Layers in Petromyzon. 



By 



S. Malta, 



Zoulugical Laboratory, Science Collège. 



With Plates XIII. ami XIV. 



In spite of the fact that .se\eral eininent investigator« have lu^en 

 eno-ao-ecl in studyino- the enihryoloo-y of the Cyclostoinata, the develop- 

 ment of Petromyzon presents as yet many points ^vhich remain 

 obscure or which are stated in contradictory terms ])y different writers. 

 The present investigation was undertaken to throw hght on some of 

 these points. It was carried on during the academic year of 1890-91 

 in tlie Zoological Laboratory of the Science Cc^llege, under the su[)er- 

 .vision of Prof-^. K. .Mitsukuri and I. Ijimn. I may, in ihis ])]ace, be 

 permitted to express my sincere thanks for tlu" vahial)le advice winch 

 they have o-i\en during my work, and the kind manner in wliich they 

 have forwarded my researches. 



The species which I have studied is prt)b;il)ly either l\(ron}tjzon. 

 planevl or a variety of it. The larger part of tlie materisds used was 

 collected and preserved l^y Prof. Mitsukuri during the month (jf Feljru- 

 ary, 1890, in fresh- water streamlets ])et\veen paddy-fields near the t(jwn 



