364 D. J. SCOURFIELD ON THE LOCOMOTION OF 



of antennae. In many cases these organs are very powerful, 

 so that, aided by an elongated and compressed form of body, the 

 progression of these little animals may be very rapid. The 

 direction of the stroke of the antennae, at least in the genera 

 Daphnia and Simocephalus, has been found to be slightly oblique 

 to the axis of the body, having a slight inclination towards the 

 oack — a circumstance which gives rise to a tendency for the 

 locomotion to take place in a curved path. This, however, is 

 counteracted partly by the action of gravity on the body between 

 the strokes, and also probably by the resistance offered to the 

 turning movement by the long shell-spines which most of the 

 more rapid swimmers possess. 



But it is among the Copepods or " oar-footed " Entomostraca 

 that the most elaborate natatory appliances exist. The four 

 or five pairs of feet are usually broad, two-branched, paddle-like 

 organs provided with fringing hairs and feathered spines. They 

 can be jerked backwards with extreme rapidity, at the same time 

 spreading out laterally in various degrees so as to present a 

 greater surface to the water. The first pair of antennae can 

 also be suddenly reflexed, and may no doubt help in locomotion 

 in some cases, although probably not usually concerned in this 

 matter. The tail, however, with its feathered setae pretty 

 certainly assists in locomotion, but its exact action requires 

 further investigation. In addition to these three sets of loco- 

 motor appendages, the members of one family, Calanidae, have 

 yet a fourth means of progression, namely, by the very rapid 

 vibration of their second antennae and maxillae, by means of 

 which a graceful gliding motion is produced. 



There are several kinds of locomotion exhibited bv minute 

 organisms found in water which have not been alluded to in 

 the foregoing remarks, either because they are at present quite 

 unexplained or very imperfectly understood. As examples may 

 be cited the movements of Diatoms, Desmids, and Oscillatoria. 

 Many attempts have, indeed, been made to explain some 

 of these movements, especially by Lauterborn .in connection 

 with Diatoms, but the matter is still involved in much un- 

 certainty. 



In conclusion, it may be pointed out that the whole subject of 

 locomotion among microscopic aquatic forms of life is one which 

 still offers a fruitful field for study. Not only are additional 



