278 Transactions of the Society. 



Of sense-organs there are on the head, first of all, two pairs of 

 styles, which are really clusters of long, fine, stiff setae. The 

 outer pair are the largest and most prominent, arising from a 

 small triangular fleshy flap, and can be followed for some distance 

 within a muscular sheath in the head, to which a nerve-thread is 

 attached. The inner pair is smaller, more dorsal in position, and 

 situated immediately below the ciliary wreath. On the ventral 

 side of the head, on each side of the mouth, there are two setigerous 

 pimples, each bearing two short styles. These are not seen from 

 a dorsal view. Then, right in the middle of the front of the head, 

 are the two characteristic fleshy prominences already mentioned, 

 surmounted by a fan of short, stiff sense-hairs. A nerve-thread 

 with ganglionic enlargement can be seen within the prominences. 

 The dorsal antenna, seated on an eminence just above the eye, is 

 quite large and prominent when seen from the front or side, but 

 is not readily observed when looked at from a dorsal view; it 

 seems to be a double organ fused into one, as two rocket-shaped 

 nerve-threads are seen to converge to it. The lateral antennae 

 were thought to be absent altogether by all previous observers. 

 For a long time I searched for them in vain up and down the sides 

 of the body, and could not understand why so large a rotifer 

 should be without these sense-organs, so characteristic of the entire 

 class. About two years ago I had received some dried pond mud 

 from Australia, and placing this in water, in a few days a solitary 

 Synchceta pectinata made its appearance from some dormant egg, 

 which shows at the same time how rotifers can be transported 

 from one distant continent to another. On examining this pale, 

 very transparent individual with quite a low power under dark- 

 ground illumination, it slowly turned round on its longer axis, 

 when suddenly I noticed a fine brush of long setae protruding 

 from the side of the body on a level with the stomach. On further 

 investigation of this strange appearance, which I had searched for 

 many times with low and high powers and with the very best 

 optical means, I found that the lateral antennae are quite obvious, 

 but situated on the ventral side of the body, and therefore are 

 quite invisible from a dorsal view, the position in which I, and no 

 doubt everybody else, had always searched for them. In the 

 figure their position at the sides is indicated, but it must be re- 

 membered that they are situated just round the corner on the 

 ventral side. 



The mouth is not oval, as has been stated, but shield-shaped, 

 and quite straight on the upper side. On the upper, and on each 

 lateral side there is a cushion of grey protoplasm, from which 

 arise a single row of very fine, short, stiff setae, which curve over 

 the mouth, meeting in the centre, and thus form a screen through 

 which all food-particles must pass. This very fine dome-shaped 

 screen is seen well only in a front view of the head under a high 



