No. 2.] STOLONIZATION IN AUTOLYTUS VARIANS. 2S5 



ber of setae are concerned, and differs but little in size. The 

 dorsal cirrus (d.c.) is, however, placed a little more dorsally 

 than that of the parent stock, and between the dorsal cirrus 

 and this ventral branch of the parapodium a new growth of 

 tissue {d.r.) is arising. This new growth is the rudiment of the 

 dorsal branch of the parapodium and becomes visible for the 

 first time in a stolon of this stage of development. 



In a dorsal view the appearance of the head has remained 

 unchanged, except that the anterior eyes have approached more 

 closely the lateral margin of the head. The shifting in posi- 

 tion of the anterior eyes at this stage is very slight, but still 

 sufficient to mark the beginning of important changes that are 

 about to make their appearance in stolons of this size. These 

 changes consist in the gradual outward shifting of the anterior 

 eyes, in process of which they are first carried laterally, then ven- 

 trally, until finally in the free-swimming individual they occupy 

 a position directly ventral to the posterior eyes. The shifting, 

 as we will see later in the study of transverse sections of this 

 region, is due to the large increase in the number of nerve cells 

 in the middle region of the head, the region occupied by the 

 eyes being in consequence carried successively lateral and ven- 

 tralward. In a lateral view of a stolon a little more mature 

 (PI. XIII, Fig. 11), the anterior eyes [e.a.) occupy a lateral posi- 

 tion, and the changes in the contour of the head have been 

 such as to bring the anterior and the posterior eyes nearer a 

 transverse line with one another. The appendages of the head 

 of stolon 4 have increased considerably in size, the dorsal 

 median tentacle reaching as far back as the sixth setigerous 

 segment, while the anterior lateral, besides elongating, have 

 also increased in thickness and are bifurcated for more than 

 one-half their length. The outlines of the buccal segment 

 have not as yet appeared dorsally, although the dorsal tentacu- 

 lar cirri (d.t) have attained a considerable length. In a lateral 

 view of the slightly older stolon, represented in Fig. 11, this 

 segment is quite well marked, and besides the presence of the 

 now elongated dorsal tentacular cirri {d.t), a rudimentary ven- 

 tral tentacular cirrus {y.t) has also made its appearance. In 

 this figure may also be noticed the region of separation {r.s.), 



