ANATOMY AND PHYSIOLOGY OF PATELLA. VULGATA. 6 29 



stain, and exhibiting a nucleolus in its interior. These fibres are collected in 

 bundles, and among them, i.e., between the individual fibres, are a number of 

 bipolar spindle- shaped cells. These cells are provided with nucleus, nucleolus, 

 and a small quantity of granular protoplasm prolonged at either end of the 

 spindle into long and delicate threads (CLII. fig. 51). 



Both cells and fibres are enclosed in a sheath of ordinary connective tissue, 

 usually one cell thick. The nuclei of the connective tissue corpuscles and 

 fibres are very evident, and quite distinguishable from the nuclei belonging to 

 the nervous elements. 



The ganglia are composed of a framework of neuroglia of the ordinary 

 nature (a very delicate connective tissue), with a very large number of nerve 

 cells. The great majority of these cells are small triangular or irregular masses 

 of protoplasm, with short branching or unbranched processes. The cells con- 

 tain nuclei and nucleoli, and take on a deep stain. 



The cells are usually much more abundant towards the surface of the 

 ganglia, and this is more especially the case with the cerebral ganglia. The 

 cells (round) also run up the sides of the principal nerves for a short distance 

 as a distinct layer beneath the sheath. 



In some places, more especially in the pedal and visceral ganglia, there is 

 an abundant admixture of long bipolar cells. This may be owing to the almost 

 undifferentiated nature of the ganglia and commissures in that situation. The 

 author has not been able to ascertain definitely the connection between the cells 

 of the ganglion and fibres of the nerve. 



In some positions, notably in some parts of the pedal and visceral ganglia, 

 and also in the buccal ganglia and their longitudinal commissures, there are 

 present a number of yellow or orange granules, which appear to be immediately 

 within the connective tissue sheath. These give to the parts where they are 

 present a yellowish-orange hue. 



Touch. — The special organs of touch are the tentacles — two in number — 

 situated on the right and left sides of the neck. Each in its contracted condi- 

 tion is about ^ inch in length, but it may be extended to from four to eight 

 times that length. At the base they are about T ^ inch in diameter, and taper 

 to a bluntish point. When examined with a hand lens, they appear corrugated 

 and pigmented, especially towards the tip. About -^ inch from the base, a 

 small pit can be made out, on the outer aspect of either tentacle. The pit 

 is filled with pigment, and has its open mouth pointing towards the tip of 

 the tentacle. It is ocular in function, and is described below. The tentacle 

 consists essentially of a mass of connective tissue in which are embedded 

 longitudinal and transverse muscular bundles. In the centre are one or 

 more nerves. The outer surface of the tentacle is covered by epithelium, 

 consisting of a single layer of columnar cells (PI. CXLIX. figs. 10 and 11). 



