334 A. J. Goldjarh 



found near the basal region of stems. Careful measurements of 

 the diameter of the coenosarc at different levels of large stems 

 actually shows that normally the diameter of the coenosarc de- 

 creases toward the distal end and conversely increases basally. 

 The relation between size and the number of hydranths regen- 

 erated, particularly at the basal end is shown by the following ob- 

 servation. Pieces less than i mm. long never produced a complete 

 polyp, though they often regenerated shoots at one or both ends. 

 Pieces as small as two-fifths mm. long developed shoots at one 

 end. Larger pieces i to 2 mm. long may regenerate one polyp at 

 each end though usually at the basal end only. Still larger pieces 

 regenerated two or three polyps from one basal end, whereas larger 

 median or basal pieces produced as many as nine polyps from 

 a single basal end. 



STOLON FORMATION 



Little has bden said concerning stolon formation, partly because 

 of its comparative rarity, partly because stolons are often with 

 difficulty distinguished from branches. A stolon," root, or hydro- 

 rhiza is an outgrowth, positively geotropic and stereotropic in its 

 reaction, which, when young, fastens itself by a sticky secretion 

 to solid objects, and which does not directly give rise to polyps. 

 In nature the stolon or stolon system anchors the hydroid. Less 

 frequently, stolons may join two stems and sometimes the coeno- 

 sarc of stolon and stem may fuse.^^ In the laboratory, stolons 

 may appear at any of the cut ends. Though most frequently 

 observed at the basal, they may appear at any lateral or even 

 oral end, singly or in groups of branching stolons. They may 

 appear simultaneously at the oral and basal ends, or at one end 

 only. The stolon may sometimes grow to a great length; in 

 one instance a stem 27 mm. long regenerated a basal stolon 40 mm. 

 long. Stolons may give rise to lateral branches usually pinnately 

 arranged, which like pedicels end in hydranths. Some un- 

 branched stolons after a time bend at their very ends and regen- 



'^The production of stolons has been shown in some species to be determined by gravity (Loeb '91). 

 in others by regional peculiarities (Stevens '02), contact (Loeb), exhaustion (Driesch), by the kind of 

 regeneration at the opposite end of piece (Morgan '01). 



^^See Stevens 'o;. 



