and the Etnhryology of Autolysis cornutus. 397 



fig. 6). The lower tubercle (A) (PI. IX., fig. 3,) is more 

 developed, and the bristles are placed nearer the dorsal 

 cirrus, than is seen in that fi2[urc. 



This lower tubercle is proportionally well developed in 

 the anterior rings, diminishing in size as the dorsal cirrus be- 

 comes smaller. The dorsal cirri are much flatter and more 

 pointed than is the case with the sexual individuals. We 

 find, also, a great difference in the alimentary canal of the 

 parent stock ; the anterior portion is specialized to a de- 

 gree which does not exist in the males and females ; where 

 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 individual while they were 

 still attached. We have in the parent stock a narrow 

 tube (oesophagus), winding from the mouth to a kind of 

 true stomach, (PI. XL, fig. 9) ; thence the alimentary canal 

 passes as a wide, almost straight, tube through the whole 

 length of the body. 



The parent stock has from forty to forty-five rings be- 

 fore the swelling which eventually forms the head of the 

 sexual individual can be distinguished. This swelling, 

 without exception, is found on the upper side of the thir- 

 teenth or fourteenth ring, or one of the adjacent rings, 

 (PI. IX., fig. 9) ; and I have never seen a single case among 

 the great number which I have observed, where this swell- 

 ing of the head appeared in any other place. As a gen- 

 eral rule, it was on the thirteenth ring that the head was 

 developed. As the central swelling increases, there are 

 formed on the two sides of this ring (see PI. IX., fig. 11,) 

 two additional swellings, (a', a")^ which soon become as 

 large as the middle one. They increase in size very rap- 

 idly, and soon outstrip the middle swelling, (PI. IX., fig. 12). 

 These three swellings are the tentacles of the head. The 

 large eye next makes its appearance, (PI. IX., 13, 6), and 

 also the dorsal cirrus {c'). After this has reached the 



