74 WILLIAM MORTON WHEELER, 



two originally discrete systems of organs may have been brought about 

 after the abolition of the atrial cavity. Then the gonadic pouches 

 instead of dehiscing directly through the skin of the animal, as is 

 still the case in Amphioxus, allowed their products to escape into 

 the body cavity and pass out through the abdominal pores, openings of 

 unknown morphological origin. This is the stage still retained in 

 Cyclostomes. The conditions which led to the present condition in 

 Gnathostomes , in which the gonads utilize portions of the nephric 

 system as conduits, are at present inscrutable, and speculation is of 

 little avail till the morphology of that neglected structure, the Miil- 

 lerian duct has been subjected to careful comparative study throughout 

 the Gnathostome division. I can see no force in the reasons adduced 

 by Semon (1892, p. 178) for regarding the separation of the repro- 

 ductive and excretory systems in Cyclostomes as secondary ; concerning 

 the manner in which the connection may have been brought about in 

 the Gnathostomes, Semon's speculations are, perhaps, as good as any 

 that have been advanced. 



e) Some General Remarks on the "Gonotome" of 

 Vertebrates. 



Returning in conclusion to a consideration of the reproductive or- 

 gans, we find considerable difierence of opinion respecting the existence 

 of a true gonotome in Vertebrates. The term gonotome (gononephrotome 

 of RüCKERT, 1888, p. 205) was introduced by Van \Yijhe, who says 

 (1889, p. 466): „Den Ausdruck Gonotom entnehme ich der Arbeit von 

 RÜCKERT, in welcher von Gononephrotom die Rede ist. Rückert's 

 Entdeckung, dass die Geschlechtsdrüsen also segmentirt auftreten, ist 

 wichtig in Hinblick auf Amphioxus, welches Thier also auch in der 

 Anordnung jener Drüsen bleibend einen Zustand repräsentirt, der bei 

 höhern Organismen nur in Entwicklungstadien gefunden wird." This 

 attempt to trace the reproductive organs of Craniota back to a meta- 

 meric condition in the embryo has been repudiated by Minot (1894) 

 who makes the statement that the large clear cells designated prim- 

 ordial ova (Ureier) by Rückert, Van Wijhe and others, are nothing 

 more nor less than dividing cells without any necessary relation to 

 reproduction. He believes that their peculiar appearance and large 

 size are thus explained ! The absurdity of this view has been condignly 

 criticized by Rabl (1896), who, however, agrees with Minot to the 



