82 STYLARIA PALUDOSA. 



setae, both hooked and filiform, very closely set together, and 

 differing from the others only in their minute size ; the fiUform 

 ones, however, being confined to the portion preceding the 

 constriction, which Mr. Baily told me was the point of division of 

 the worm. The intestine, it should be noted, is continued past 

 the constriction ; though the glandular covering, which elsewhere, 

 as in Tubifex, gives it its colour, is here deficient — a deficiency 

 which is again apparent in the anterior segments. On the 27 th, I 

 found the small setae, which had previously been difircult to make 

 out, longer and much more clearly marked. The intestine was 

 continuous as before, but, iriirabile dictu, a new proboscis was 

 seen immediately below the constriction, waving about as if to 

 feel the surrounding objects, exactly as did its prototype (see Fig. 

 2). Also, a pair of new eye-spots were distinctly visible, and 

 something very much like a new pharynx adjoining the intestine ; 

 but of this last observation I am not quite sure. On the 28th 

 my worm had divided, and become two perfect worms : I did not, 

 indeed, as Mr. Baily had done, see the separation, but the fact 

 was placed beyond all dispute. The process evidently consists of 

 the interposition of a number of new segments, both above and 

 below the point of separation ; these being at first, as might be 

 expected, much crowded together, as indicated by the minute size 

 and close setting of the new setae, which gradually grow and 

 separate from one another as differentiation proceeds. Inasmuch 

 as no new filiform setae are produced below the separation, this is 

 in exact conformity with the type of the original, which requires 

 the absence of these setae from the anterior portion of the new 

 worm produced by the fission. By the absence, again, of the 

 glandular covering of the intestine in the new segments posterior 

 to the constriction, provision is made for the reproduction of this 

 feature also in the new being. The intestine itself appears to 

 remain entire till the moment of separation ; for, on comparing 

 the new worm with the original, it is at once seen that the mouth 

 of the former is as yet imperfect, requiring time for its complete 

 development (see Plate 8, Figs. 3 and 4). 



Dr. Carpenter * gives the following details concerning the 

 fission of Nais : — " After the number of segments of the body 

 has been greatly multiplied by gemmation, a separation of those 

 of the posterior portion begins to take place ; a constriction forms 

 itself about tlie beginning of the posterior third of the body, in 

 front of which the alimentary canal undergoes a dilatation, while 

 on the segment behind it a proboscis and eyes are developed, so 

 as to form the head of the young animal, which is to be budded 

 off; and in due time, by the narrowing of the constriction, a 



* Principles of Physiology, 3rd ed., p. 934, par. 714a. 



