[ 281 ] 



IX. On the Variations m the Internal Anatomy of the Gamasinse, especially in that of 

 the Genital Organs, and on their Mode of Coition. By A. D. Michael, F.L.S., 

 F.Z.S., F.B.M.S. 



(Plates XXXII.-XXXV.) 



Read 3rd March, 1892. 



Contents. 



Page 

 Introductory ( Observations 281 



Bibliography 282 



Objects of this Paper 285 



Modes of Investigation _ 286 



The Species used 287 



The Male Genital System 289 



The Mode of Coition 294 



The Female Genital System 297 



The Alimentary Canal 309 



Excretory Organs 311 



Musculation 311 



Summary 31 ] 



Descriptions of New Species 312 



Explanation of the Plates 317 



Introductory Observations. 



J. HIS paper records the results of a series of investigations extending over the whole 

 of the years 1890 and 1891 and the early part of the year 1892. They have been 

 conducted partly in London, through the kindness of friends, from whom I have 

 received frequent supplies of fresh material from which I could obtain living specimens 

 of the various species I was studying ; partly at the Land's End, Cornwall, during an 

 autumnal stay there ; partly near Ragaz, in Switzerland, during the summer of 1890 ; 

 and partly near Innsbruck, in Tyrol, during the summer of 1891. In the two last- 

 named localities I had the advantage of conducting the work jointly with my cousin, 

 Mr. M. J. Michael, who has cut the very numerous serial sections which have formed 

 one of the methods of investigation ; he also drew fig. 68. In Tyrol I also had the 

 assistance of Mr. E. Bostock, of Stone, in collecting specimens. I beg to tender my 

 thanks to both those srentlemen. 



This paper is not intended as a general treatise upon the anatomy of the Gamasinte • 

 it is confined, as strictly as may be, to those parts which I believe to be new or to varv 

 from existing records — previously-known organs, which do not vary, being only so far 

 referred to as seems to me desirable in order that the new matter may be clearly under - 



SECOND SERIES. — ZOOLOGY, VOL. V. 42 



