THE REPKODUCTION OF ANNELIDS. 371 



first two or three rings, and then on the others, and become frequently 

 changed into Aprsal cirri, and by the time the last dorsal cirrus is 

 developed, the middle tentacle has again outgrown the lateral tentacles, 

 the tentacular cirrus has been developed, and the annelid has all the 

 appearance of a parent stock with short cirri. From this stage the 

 development goes on very raj^idly, the number of rings increases very 

 fast, and in a few weeks the embryo has passed through all its stages — 

 has reached its full size, and is ready to begin the reproduction by 

 division ; it is now called the parent stock. This ' parent stock ' has 

 the same colour as the males and females : the tentacles of the head are 

 like those of the female, the middle one being longer ; in place of the 

 large well developed eyes of the males or females, we find but two 

 large and two small accumulations of pigment cells : the rings are 

 provided with but one kind of bristle. There is also a great difference 

 in the alimentary canal, the anterior portion of which is specialized to 

 a degree which does not exist in the sexual individuals, in whicn the 

 alimentary canal is simply the cutting off" of a portion of the tube 

 forming the common digestive cavity of the parent stock and the 

 sexual zooid while this is still attached to the parent stock. There 

 is a narrow oesophagus winding from the mouth to a true stomach. 

 Thence the alimentary canal passes as a wide, almost straight tube 

 through the whole length of the body. "When fully developed the 

 parent stock has from 40 to 45 rings. On the upper side of the 

 13th or 14th ring, most generally the former, a swelling is found, which 

 eventually becomes the head of the sexual zooid. As the central 

 swelling increases, there wlU be found two additional ones on the 

 sides, these three swellings are the tentacles of the head. The large 

 eye next makes its appearance, and then the dorsal cirrus. After this 

 has reached a certain length, the second eye can be seen. Tracing 

 the development further we find there is a marked difference in the 

 growth of the tentacles in parent stocks which are otherwise identical. 

 This is on account of the difference in sex of the zooids, the male 

 and female tentacles being developed in a totally different manner. 

 The rings following the head (five in males and six in females) 

 undergo scarcely any change, but in the succeeding rings, the dorsal 

 cirri increase still more in length, a slight protuberance is formed 

 immediately below the dorsal cirrus, from which a bundle of fine 

 needle-like bristles are developed ; thus the anterior rings have two 

 bunches of bristles, as in the adult males and females, and the upper 

 bunch attains its full size before the young separates from the parent 



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