No. 2.] STOLONIZATION IN AUTOLYTUS VARIANS. 29 1 



processes of stolonization take place. As the principal phenom- 

 ena are those which are connected with the development of the 

 head and buccal segment, while those concerned in the devel- 

 opment of the remaining portion of the body present no impor- 

 tant characteristics different from direct development among 

 Syllidians, a section of the anterior segments of a mature 

 stolon will present all the important structures concerned in 

 the process of stolonization. 



PL XIII, Fig. 14, represents a longitudinal median section 

 through the head, buccal, and the anterior part of the first setig- 

 erous segments of a mature male stolon. The first setigerous 

 {sg.\) and buccal segments {b.sg) are separated by a distinct 

 dissepiment {dis). Between the buccal segment and the head 

 the musculature of the dorsal median tentacle (/.wz.) forms the 

 only partition, and laterally where these fibers do not exist, the 

 coelomic cavity of the buccal segment extends forward into 

 the tissues of the head for a short distance, so that internally 

 these two regions are not so distinctly separated, Dorsally, as 

 well as laterally, the body-wall of the buccal and setigerous 

 segments consists of an epidermis covered by a thin cuticle 

 (cit^j and overlying a layer of circular and longitudinal muscle 

 fibers. The epidermis {ect) consists of a single layer of cells 

 distinctly separated from the underlying tissues, and its out- 

 lines are clearly defined. Ventrally, however, the epidermal 

 cells are very indistinctly outlined, and, particularly in the 

 regions of the ganglia of the ventral cord, are so intimately 

 associated with the ganglion cells {c.n.) of the ventral cord that 

 the epidermis cannot be distinguished from the underlying 

 tissues by means of the ordinary methods of preparation. 

 The endodermal cells, as they approach the mouth-opening (<?), 

 become smaller, and where this structure joins the ectoderm 

 the outlines of the cells are lost. The body space of the first 

 setigerous segment is filled with sperm cells. The cavity of 

 the buccal segment also contains sperm cells {s.p), but they 

 are usually fewer in number and less compact. 



The head {c) is an almost solid structure, its only cavity 

 being the space on either side of the muscles of the dorsal 

 median tentacle, which is in reality a forward extension of the 



