344 



— the oviduct ; the interior of the ovary was divided into numerous 

 compartments by trahecula arising from the external coat and anasto- 

 mosing with each other : toAvards the inferior surface of the organ these 

 compartments which contained numerous ova in various stages of de- 

 velopment, became fused together and were perfectly continuous with 

 the wide lumen of the oviduct. It is impossible to state the exact point 

 where the ovary ends and the oviduct commences. I hope later on to 

 give fuller details respecting the structure of the ovary but at present 

 content myself with emphasizing the fact that the oviduct is per- 

 fectly continuous with the ovary. This is novel to the whole 

 group of the Chaetopoda; in many cases there are no special oviducts; 

 when present they are completely indépendant of the ovaries, being 

 in all probability the equivalents of nephridia. On the other hand in the 

 Platyhelminthes and Leeches the ovaries and oviducts are continuous 

 structures precisely as they are in Eticlrilus. Even if there is not the 

 profound morphological distinction between the two forms of genera- 

 tive glands and ducts as is believed by the brothers H er twig (»Coelom- 

 theorie«), among others, to exist, there is a striking anatomical diffe- 

 rence ; it is of importance to note that, as far as the female reproduc- 

 tive apparatus is concerned, the Oligochaeta may possess generative 

 organs which depart widely from the structures characteristic of the 

 group and'agree in many points with the Platyhelminthes, Leeches, and 

 even some of the Mollusca. 



Although the structure of the female organs of Eudrilus is so re- 

 markable, and as far as is at present known unique in the group to 

 which it belongs, the male organs conform to the ordinary type; there 

 are three pairs of testes (probably vesiculae séminales as in Lumhricus), 

 and two vasa deferentia on either side which open on to the exterior 

 of the body on the 17th segment. The accessory glandular organs 

 connected, with the external orifice of the vasa deferentia, have been 

 accurately described by Mr, Per ri er. 



4. Zur Geschichte der Vererbungstheorien. 



Von Dr. August Weismann, Professor in Freiburg. 



cingeg. 4. April 1886. 

 »Selten nur ist ein fruchtbarer Gedanke in der Wissenschaft auf- 

 getaucht, ohne daß er nicht von einer Seite bekämpft , von anderer 

 aber als bereits bekannt hingestellt worden wäre. Das Erstere ist ge- 

 wiß vollkommen in der Ordnung, ja sogar nothwendig, denn erst aus 

 dem Kampf der Meinungen kann die Wahrheit klar und bestimmt 

 hervorgehen, aber auch dem ZAveiten ist nicht alle Berechtigung ab- 



