722 William Patten ' 



g-one by the au ditory and visual cells, be converted into cells especially 

 sensitive to these clianges. 



We bave already seen bow Constant tbe two kinds of cells are in 

 tbe lower forms of eyes , and bow a single or compound sense celi is 

 surrounded by pigmented ones. A remarkable similarity maybe found 

 in tbe arrangement of tbose sense cells supposed to bave tbe function 

 of testing tbe cbemical composition of tbe vt^ater. 



Over a year ago , before tbe present paper v^as tbougbt of, I made 

 some studies upon tbe sense papillae of Mollusca , especially of Pecten 

 and Haliotis, and, in looking over tbe drawings tben made , I find tbat 

 tbey confimi, in general, my couclusion conceruiug tbe structure and 

 Innervation of tbe sense cells, and tbeir graduai transformation into 

 ganglionic ones. Tbere are several points wbicb I desire to examine 

 once more before publication, but one or two facts will be of interest to 

 US bere. In Haliofis, eacb papilla eontains a centrai coreoftwelve 

 sense cells ending inwardly in as many single fibrous prolongations, 

 wbile tbeir distai e^tremities, just beneatb tbe tip of tbe papilla, are 

 fused into a single, protoplasmic mass. Tbe tip of tbe papilla is sur- 

 rounded by a perfect circle of numerous, stiff sense bairs, eacb of wbicb 

 is connected witb tbe fused ends of tbe sense cells by a minute fibre. 

 Tbe wall of tbe papilla is clotbed witb trumpet-sbaped sense cells end- 

 ing in single fìbres. Eacb papilla also eontains 8 very large, club-sbaped 

 and gland-like cells filled witb innumerable, but distinct, refractive 

 bodies , and extending tbe wbole lengtb of tbe papilla , terminating- at 

 tbe outer extremity in a bent end. Tbey form a not very compactly 

 arranged circle arouud tbe centrai core of sense cells. 



In Pecten, tbe papillae are essentially of tbe same structure, but 

 smailer. Tbe buucb of sense cells is reduced to eigbt, wbile tbere is 

 only one large gland-like celi. 



In Lima, tbere are no sense papillae, but tbe long tentacles contain 

 rings of sensory and gland cells, witb smootb intervening Spaces, wbicb 

 cause ajointed appearance. Some of tbe gland-like cells are enormous, 

 and are usually arranged in twos ; between tbeir outer ends is a minute 

 sense celi ending, externally, in a tuft of stiff bairs, and inwardly 

 in a long fibre. Tbe sense celi is tberefore enclosed in a circle of two, 

 large gland cells. 



In tbe organs of taste, and in tbe sense organs of tbe lateral line, 

 tbe sense bair cells are usually arranged in groups, surrounded by 

 circles of large gland-like cells, often called support cells. Tbe almost 

 Constant, if not universal association of these gland cells, witb sensory 



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