66 Journal of Comparative Neurology. 



demonstrated beyond question the existence of two epiphysial 

 outgrowths in Coregonus, Salmo, Catostomus, Stizostedion, 

 Lepomis and Hkewise in the Ganoid, Amia. 



In three of these forms ( Catostomus, Stizostedion, Lep- 

 omis ) single stages as observed in the living larvae are de- 

 scribed. The remaining forms were studied in serial sections. 

 In a single form ( Coregonus ) the author describes the origin of 

 of the two vesicles. They are here found to "arise as separate 

 outgrowths from the roof of the brain" . . . "the opening of 

 the anterior vesicle is a little more in front of the opening of 

 the posterior than to the left of it." 



In Salmo, the form most carefully studied and on which 

 the greatest emphasis is laid, the author did not observe the 

 origin of either the posterior or anterior vesicle. The earliest 

 condition studied in sections is one in which "the two vesicles 

 are attached to the brain-roof by a common stalk." "These ves- 

 icles may have been formed in any one of three ways: (i) 

 They may be thought of as independent and separate out- 

 growths which have subsequently come to be borne on a com- 

 mon evagination of the brain roof; (2) it is possible to think of 

 them as formed by the division of an originally single vesicle; 

 (3) it is possible to think of the anterior as formed by constriction 

 from the posterior." The author explicitly states that he has 

 not obtained satisfactory sections of stages younger than that 

 above described and " if one judges by this figure alone there 

 is little to choose between the three methods of origin men- 

 tioned above." There is one observation recorded by Hill 

 which deserves special mention. In a Hving embryo 37 days 

 old the author found two distinct elevations of the outer sur- 

 face and "beneath each of these was a slit-like lumen leading 

 from the brain cavity toward the outer surface of the brain wall. 

 These lumina are entirely separate from one another. " The 

 author further states that : "unfortunately this observation was 

 made on but one living individual and, owing probably to the 

 rapidity with which the stage is passed through, I was unable 

 to verify it on others." The fact that the author was unable to 

 confirm the observation on other larvae coupled with the unsat- 



i 



