264 The Microscope. 



may be does not appaar. They are probably tactile, and, it may be, 

 protective. Without them the dorsal surface would be naked, except 

 for the presence of two fine, almost vertical, tactile hairs on the 

 posterior region, each of these arising from a minute papilla near the 

 lateral borders. 



The ventral surface is usually ^nd obstinately kept in contact 

 with the submerged object, or at least directed toward the surface 

 above which the animal is swimming; the part is therefore not easily 

 examined, as the obsei'ver must wait until the animal thinks it proper 

 to turn on its back, a position it seems to dislike, for the evident 

 reason that it has four springing setse on the ventral surface, by 

 whose action it makes some surprising leaps. It is not possible to 

 reverse the slide, as the thickness of the glass forbids the use of the 

 high-power objective needed, for this Dasydyte^ is only ^ig- inch 

 long, an ^th inch objective being necessary for its study. 



The ventral cilia are long, fine and comparatively few in num- 

 ber. They are in two bands extending longitudinally near the 

 lateral margins, essentially as in most species of Chcetonoiiis. The 

 central region between the bands appears to be clothed with short, 

 fine, immotile setse, a somewhat similar arrangement being also 

 present in several forms of Chcetonotus. Near the centre of this 

 region of the body proper there originate four setae, two long and 

 two short, the longest much exceeding the whole animal in length, 

 the setoe of both groups projecting far beyond the posterior body- 

 margin. They originate as do the dorso-lateral appendages, directly 

 from the cuticular surface, and have the irregularly sigmoid curva- 

 ture near the base. These are the springing setse already spoken of, 

 and their elbow-like basal curvature is the only unevenness in any 

 part, the portion beyond it tapering gradually to the end. 



The evenly swimming movements of Dasydytes are somewhat 

 more rapid that those of Cha'tonotus, but the former has the addi- 

 tional ability to suddenly leap to one side, by means, as I suppose, 

 of these long ventral setse, often unexpectedly jumping to a distance 

 exceeding twice its own length, and disappearing from the field. 

 For this reason I have named the species Dasydytes saltitans, sp. 

 nov. The leaps are made so suddenly that the exact method is invis- 

 ible. They are probably accomplished, however, by the movement 

 of these four set;e, together or separately, the leap being caused by 

 the recoil and the reaction of the water. 



