257 
he went into this matter yet more carefully. His views, which were 
in the main shared by MERKEL (’79) and many other careful investig- 
ators, were to the effect that a bundle of medullated nerve fibres 
entered the base of each organ, losing there their medullary sheaths; 
that these fibres then subdivided and interlaced to a greater or less 
extent, and that finally each, or some, of these fibrillations entered 
directly into the base of a pear-shaped sensory cell, from the apex 
of which a bristle projected free into the lumen of the canal. 
On the other hand, some of the more recent investigators of the 
anatomy of the nervous system, among them Rerzıus (92) and LEN- 
HOSSEK (92 and ’93), working by the GoLGI methods, have expressed 
their belief that in these organs the nerves terminate not in sensory 
cells, but in free fibrillations. However, LENHOSSEK and Rerzius are 
not entirely in agreement as to whether the nerve fibrillations pene- 
trate between the cells comprising the sensory bud. 
In the hope of getting further evidence as to which of these 
views was the correct one, the writer, working under the direction of 
Professor E. L. Mark, undertook the investigation of which the fol- 
lowing is a summary. The work has been carried on in the Zoölogical 
Laboratory of the Museum of Comparative Zoölogy, Cambridge, Mass. 
The material used was the common bullhead, Ameiurus nebulosus 
LE Surur. This fish seemed especially adapted to work of this kind, 
on account of the absence of scales. 
In order to get a correct idea of the topography of the sense 
organs of the lateral line, preparations were first made by fixing 
pieces of skin and subjacent muscle which included the lateral line in 
vom RATH’s picro-osmic-platino-acetic mixture for one hour and a 
half. This material was subsequently treated exactly as directed by 
vom RatH (95, p. 282—285). Sections cut transversely to the canal 
and those cut lengthwise of the canal and perpendicularly to the sur- 
face of the body both showed essentially the same features. The 
round or oval, flat-topped sensory organ is separated from the adja- 
cent epithelial lining of the canal by a basement membrane. On this 
rests a layer of indifferent sustentative cells, some of which are pro- 
longed as thin, flat processes between the sensory cells. The latter 
are pear-shaped and arranged with regularity in the superficial half 
of the organ, the broad deep end being almost as far from the base- 
ment membrane as from the outer surface; the free end of each 
sensory cell terminates in a distinct bristle, which projects into the 
lumen of the canal. By this method of treatment the sensory cells 
