328 CONTRIBUTIONS TO THE NATURAL HISTORY 



microscope. But then the fringes lie flat, and the tips of each upper comb cover the 

 bases of the lower, so that their insertion connot be well understood unless an upper 

 comb be entirely removed, as in Plate II. Fig. 6. The connection of the chymiferous 

 tubes with these vertical rows of locomotive fringes may be no obstacle in the 

 way of their study in their living, active condition, for then they are so distended 

 and so full of fluid as rather to facilitate their study, as they appear like a trans- 

 parent basis through which the external appendages are examined with great ad- 

 vantage. But when pieces are separated from the body, the tubes collapse, and 

 contract so much as to form a narrow erect hose about the middle of the vertical 

 rows, which I had for a long time taken for a particular organ, until I ascertained, by 

 repeated investigations, that it was the chymiferous tube empty and contracted. In 

 Plate II. Fig. 6, the outlines of this chymiferous tube are drawn in two different stages 

 of contraction, a and a representing its outline when half empty ; b, b, when fully con- 

 tracted. Again, vertical muscular fibres, and others crossing them at various angles, 

 near the margin of the locomotive rows, may interfere with the study of their fringes, 

 before one is fully acquainted with the subject. All these circumstances should be 

 particularly kept in mind, when examining the muscular fibres of the base of the 

 fringes, which act in moving them up and down, and which belong in their transverse 

 rows to the isolated combs proper. These are best seen from the anterior surface of the 

 rows, when a thin slice is cut in a vertical direction, and the combs themselves are 

 placed upon the objective table with their base turned upwards. Finally, there are about 

 this region other organs, tlie nature of which it has not been in my power to recognize, 

 though they are constantly seen between the locomotive combs, alternating regularly with 

 them, and placed about the third of their width. I allude to minute tubercles or gan- 

 glion-like swellings (Plate II. Fig. 6, 7, and 9, o, o), so small as to be, perhaps, simply 

 isolated cells of a special character, but which, in the midst of the tissues, I have never 

 been able fully to isolate. There are constantly two of them, or a pair, placed symmetri- 

 cally, at equal distances between the single combs. Other swellings not so constant in 

 their appearance occur in the middle line (c, c). These swellings seem to be united by 

 a vertical thread ; but this thread, as represented in Fig. 9, may be a rudiment or a fold 

 of the contracted chymiferous tube, as I never could find it equal in appearance in two 

 specimens. The swellings in this line may be particles of the harder contents of the chym- 

 iferous tubes, accumulating in the intervals of the combs, and forming little balls, when the 

 tube is finally completely contracted. But whatever may be the real nature of these bod- 

 ies, those which occur regularly in pairs are certainly of a different nature ; for I have fre- 

 quently seen distinct threads, or fibres, connected with them ; sometimes, as in Fig. 6, 



