No. 2.] STOLONIZATION IN AUTOLYTUS VARIANS. 279 



addition of a fourth segment {x), while at the same time lateral 

 outgrowths are appearing on segments i and 3 and a little 

 later on segment 2, thus presenting a stage as represented in 

 Fig. 7. 



Two regions of growth may accordingly be distinguished as 

 having been active in this early stage of development. The 

 first region is that posterior to and including the segment of 

 proliferation and has contributed three, or, in some specimens, 

 four segments to the formation of the stolon, these segments 

 forming the most anterior setigerous, the anal, and one or two 

 indifferent segments. Of these segments the anal is the old- 

 est, the others being successively younger from this segment 

 forward, while the first setigerous is, therefore, the youngest. 

 The second region of growth is anterior to and includes the 

 anal segment, and supplies new segments for the lengthening 

 of the individuals. This region in Autolytus varians does not 

 contribute to stolon A in Fig. 6, but makes its appearance at a 

 little later stage, thus not becoming active until after the out- 

 line of the stolon has been clearly defined. 



Posterior to this zone of embryonic segments in Fig. 6 is the 

 most anterior stolon (St. i), which represents in a rudimentary 

 condition all the regions of a mature stolon. This young 

 stolon consists of eight well-marked segments, the anterior 

 ones being the larger, while the posterior ones are considerably 

 smaller. The first four segments have rudimentary parapodia, 

 with small setae just appearing, and distinct dorsal cirri. The 

 fifth segment has still more rudimentary appendages, similar 

 to those of stolon A. The sixth and seventh segments are the 

 most embryonic and show no evidence of lateral appendages, 

 but present an appearance like the embryonic segments in the 

 anterior part of the chain. The eighth or anal segment has a 

 pair of caudal cirri (Fig. 8, ex.) of considerable length, the 

 development being sufficiently advanced to bear evidence of 

 the early origin of this segment. 



On the anterior dorsal half of the first segment of this stolon 

 a new region of growth (r.) has made its appearance. This is 

 the first indication of the head and consists, in a stolon of this 

 age, of merely a thickening of the tissue in the anterior half of 



