Februaby 16, 1900.] 



SCIENCE. 



251 



method is advantageous in staining deeply 

 cell boundaries and axis cylinder processes 

 in early stages. The results obtained by 

 the use of this method are : 1 . Ventral 

 nerves in Squalus and Petromyzon embryos 

 arise primarily as axis cylinder processes of 

 cells lying in the ventral horn of the neural 

 tube. 2. There are secondarily added to 

 these processes cells from two sources : (a) 

 cells which have migrated out from the 

 neural tube in the region of the root of the 

 nerve; and (6) cells from the mesenchyma 

 through which the nerve passes. At first 

 these cells take a peripheral position with 

 reference to the bundle of axis cylinder proc- 

 esses (= nerve fibers), but in later stages 

 they migrate into the midst of these proc- 

 esses. 3. The cells thus added second- 

 arily to the nerves do not form nerve fibers 

 as has been held by several investigators, 

 but form simply the primitive or Schwann's 

 sheath. The nerve' fibers are from their 

 beginnings the processes of cells lying in 

 the ventral wall of the neural tube as stated 

 above. The mode of development of the 

 medullary sheath has not been determined. 



Thus the ventral nerves of these Anam- 

 niote forms differ in their development from 

 the same nerves in Amniota only in deriving 

 some of the sheath cells from the neural 

 tube. The sheath cells in Amniota appear 

 to be derived wholly from the mesenchyma 

 (His, Kolliker and others). 



The conclusions of Balfour, von Wijhe, 

 Dohrn, Beard, Kupffer and others, that 

 cells migrate from the neural tube into the 

 ventral nerves of Amniote embryo is thus 

 confirmed. The inference that these cells 

 form the nerve fibers is not correct. 



On the existence of accessory optic vesicles, 

 based on neiv observations. W. A. Loot. 

 Read by title. 



New observations on the primary segments of 

 the vertebrate head. Charles Hill, 

 This was presented by Dr. Locy. 



The development of the adhesive organ and 



hypophysis in Amia. Jacob Eeighaed. 



(In conjunction with Miss Phelps and 



Mb. Mast.) 



An account of the development of the 

 adhesive organ appeared in the report of 

 the New York meeting (1898) of the Amer- 

 ican Morphological Society, published in 

 Science. The hypophysis develops as an 

 ectoblast thickening connected with the an- 

 terior neuropore and lying, in early stages, 

 between the neuropore and adhesive organ. 

 Its subsequent history. does not differ essen- 

 tially from that described for other verte- 

 brates by Haller. It is at no time con- 

 nected with the entoblast, and unlike the 

 hypophysis of Acipenser, does not, there- 

 fore, afford support to Kupffer's interpreta- 

 tion of the hypophysis as a paleostome. 



Exhibition of figures for a Normentafel of 

 Amia ivith an account of methods of photo- 

 graphing the embryo. Jacob Reighard. 

 The method consists in the use of a 

 long focus lens (80 mm. projection lens 

 of Leitz), together with a long camera — 

 the large photomicrographic camera of 

 Zeiss — attached to the wall vertically. 

 This arrangement allows of great focal 

 depth, together with a magnification of 

 10-20 diameters. The microscope stands 

 on a base-plate provided with leveling 

 screws. Focusing at a distance is accom- 

 plished with a device which works the 

 coarse adjustment. Reflectors for regula- 

 ting the intensity of the shadows and a 

 means of marking the embryo in order to 

 obtain a sharp focus were described. 



The breeding habits of Amia. Jacob Reig- 

 hard. 



The nests are premeditated structures 

 and are prepared sometime in advance of 

 spawning by the male fish, by biting or 

 tearing away the bottom vegetation. They 

 are not accidental, or mere concomitants of 

 the act of spawning. They may be near or 



