604 William Patten 



lai'ge, refractive, wavy fibres, which appear to bave lost (?) tbeir ner- 

 vous function. 



Tbe circum palliai nerve contains as mauy ganglionic swelliug-s 

 as tbere are optic nerves. In many, if not all, of tbese g-aug-lia, tbere 

 is a peculiar iufolcling dividing tbem into balves (fig. 10, cp. ti.]. 



Tbe free edge of tbe opbtbalmic fold contains at regulär intervals, 

 large ova-like cells, wbieb may be seen in preparations of tbe wbole 

 mantle edge, as well as in section (figs. 2 and 7). I am unable to offer 

 any Suggestion as to tbeir signification. 



In tbe neigbborbood of tbe binge, tbe brancbial wall of tbe mantle 

 of younger specimens is tbrown into a variety of tbick ciliated folds, tbe 

 nuclei of wbicb are, in most cases, several rows deep (figs. 1 and 9). 

 Tbe outer of tbese folds is occasionally tbinner and more protuberant 

 tban tbe otbers. It is likewise cbaracterized by its innumerable cilia, so 

 closely packed and equal in lengtb tbat tbey appear more like a striated 

 protoplasmic layer, tban cilia; tbey also form little tufts or groups over 

 eacb flattened celi (fig. 1). In some cases, one of tbe folds becomes 

 especially eularged at its extremity , tbe walls tbickening to form a 

 kidney-sbaped body witb a great many small, deeply stained nuclei 

 (fig. 15). Tbe surface is covered witb a cuticula provided witb minute 

 papillae, from eacb one of wbicb originates an enormously long cilium 

 continued tbrougb tbe cuticula into tbe clear cortical layer (fig. 15, a.y) . 

 Toward tbe binge, tbe opbtbalmic fold may undergo a similar cbange, 

 in tbat botb its walls become greatly tbickened and filled witb several 

 rows of small nuclei (fig. 13); in tbis instance, bowever, tbe cilia are 

 absent. Tbe tentacles are usually developed between tbe eye and tbe 

 velum, but towards tbe later stages, it often bappens tbat tbey may ori- 

 ginate at tbe base of tbe opbtbalmic fold, between it and tbe eye (fig. 7). 



Wbile in Trieste, I partially prepared a paper upon tbe sense 

 bair papillae of Mollusca, tbe publication of wbicb was delayed witb 

 tbe bope of finisbing certain observations, not as complete as I de- 

 sired. "VVbile studying tbe development of tbe eyes of Pecten, my atten- 

 tion was attracted by certain facts, concerning tbe origin of tbe tenta- 

 cular nerves and tbe sense papillae, wbicb promised to tbrow ligbt 

 upon tbe origin of tbe optic nerves. It was also necessary, for otber 

 reasons, tbat a comparison sbould be made between tbe development 

 of tbe eyes, and tbat of tbe tentacles, in orderto determine tbe relation 

 between tbe two structures, andto see wbetber, as bas been suggested, 

 tbe eyes are modified tentacles or not. 



Tbe following remarks, concerning tbe origin of tbe sense papillae, 



