914 



SCIENCE 



[N. S. Vol. XXVII. No. 702 



Each of the thousand cells does not send 

 an axone back into the brain unless these 

 fibers enter the olfactory bulb under the 

 g-uise of osmotic axones. Such Golgi and 

 Cajal preparations show morphological sim- 

 ilarities to sympathetic cells. There are 

 many points of similarity between Pinkus's 

 nerve in the bony ganoids and Locy's 

 nervus terminalis in sharks. There are two 

 ganglia in the course of the nerve in 

 Squalus acanthias and some of the cells 

 are multipolar. 



The "Primitive Pores" and the Sensory 

 Ridges of the Lateral Line of Polyodon 

 spathula: Henry F. Nachtrieb, Univer- 

 . sity of Minnesota. 



The "primitive pores" or pits. The 

 many-layered epithelium of the skin passes, 

 without change, into the mouth of each pit 

 and then gradually becomes reduced as it 

 passes toward the bottom of the pit, where 

 it consists of two layers or of two distinct 

 layers with interspersed pseudostratified 

 areas. The cells are of two distinct types. 

 The more conspicuous cells are large, clear 

 columnar cells resting upon the basement 

 membrane and containing centrally located 

 nuclei with two to six distinct nucleoli 

 (using the term in a general sense). The 

 other type is, as a rule, a more or less flat- 

 tened cell lying on the outer ends of the 

 basal cells. They fit in closely between the 

 rounded ends of the basal cells and conse- 

 quently have an uneven lower surface. For 

 convenience we may call them cover cells. 

 Each cover cell contains a large, more or 

 less irregularly shaped nucleus with, as a 

 rule, but one nucleolus. Some of these 

 cover cells clearly extend to the basement 

 membrane, and various stages between a 

 definite cover cell and a basal cell, with 

 reference to both the cytoplasm and the nu- 

 cleus, have been observed. A basal cell 

 may be completely covered or send a small 

 finger-like projection up between the con- 



tiguous covering cells, or there may be a 

 pore-like opening above it between the 

 cover cells. The cells here called basal 

 cells have been designated as suppoi-ting 

 cells and the cells corresponding to what 

 are here called cover cells have been 

 designated sense cells, thus interpreting 

 the pit as a sense organ. There are no 

 structures supporting this interpretation. 

 Well-preserved material and the elimina- 

 tion of all artifacts indicate that the primi- 

 tive pits of Polyodon are simple glands that 

 secrete a peculiar mucus-like substance. 



The sensory ridges of the lateral canal 

 are about .6 mm. long and in transverse 

 sections cover the floor (or wall next to the 

 muscles) of the canal. The epithelium is 

 a simple flat epithelium excepting in the 

 sensory ridges, where it is more or less 

 columnar and consists of two types of cells. 

 One is a relatively large clear cell resem- 

 bling the basal cells of the primitive pits. 

 These cells either do not rest on the base- 

 ment membrane at all or only through very 

 thin extensions. The other rests upon the 

 basement membrane, and is a more slender 

 and more irregularly shaped cell with a 

 distinct oval nucleus. In the neighborhood 

 of the clear cells, they generally overlap or 

 cover the outer ends of the clear cells. 

 Neither type of cell has any peculiarly 

 differentiated free surface. As in the case 

 of the primitive pits fine nerve fibrils end 

 between the cells. A more or less evident 

 network has been observed on some of the 

 denser cells, which appear to be of two 

 kinds, a supporting and a sensory cell. 

 Clear cells discharging their contents into 

 the canal are not infrequently seen in well- 

 preserved material. While hairs or hair- 

 like processes have not been definitely made 

 out on any of these cells, the innervation 

 and general appearance as well as the ex- 

 periments of Parker and others indicate 

 that these ridges are sense organs. There 

 is no evidence that the primitive pits are 



