ON A LITTLE-KNOWN SENSE-ORGAN IN SALPA. 93 



At the base of the calyx its walls are relatively thick. 

 Towards its mouth they thin down, and terminate in a 

 beautifully delicate, thin, hyaline, incurved lip (/. ca. in figs. 

 3 and 4). According to my view, both layers of cells must 

 concur in the formation of this lip, but are there indistin- 

 guishably fused together. 



Ussow does not seem to have seen the calyx at all. 



The nerve runs down the greater part of the length of the 

 stem without dividing. At or a little before its entrance into 

 the vestibule it begins to break up, first into about three 

 branches, then into about six or seven, and finally, by what 

 appears to me a strictly dichotomous mode of division, into as 

 many twigs as there are sense-cells. This last division always 

 takes place quite close to the sense-cells. 



The sense-cells are spindles of about 15fx in length and 

 5^ in breadth. They have an oval nucleus, of very compact 

 texture, somewhat basally placed, with its longer axis parallel 

 to the longer axis of the bulb. They, or at least the more peri- 

 pherally placed ones, are curved spindles, their outlines follow- 

 ing in the main the lines of the calyx, and their distal ends 

 especially being sharply bent inwards, so as to bring them 

 within the orifice of the calyx (which is frequently much nar- 

 rower than in the figures). I believe that their number is 

 constant, and that there are just fourteen of them in all. They 

 can be counted with considerable certainty in optical transverse 

 sections (see fig. 5). 



The sense-cells are embedded in a finely granular matter, 

 which may often be seen to project in a flattened dome out of 

 the mouth of the calyx {gr. in figs. 3 and 4) . I would suggest 

 that this granular matter is perhaps secreted by the inner cells 

 of the calyx. It is not figured by Ussow. 



Proximally these cells taper down gradually into their 

 respective nerve-twigs. Distally they taper down equally 

 gradually, and without the intervention of any ''granule" or 

 other apparatus of the sort, into delicate hairs. These hairs 

 are very pale, almost invisible in the living state, smooth or 

 Very delicately mottled and corrugated. They stain with great 



