332 A. J. Goldfarb 



therefore, tends to grow upward. The more coenosarc present 

 near the cut end, as determined by its width and density, the 

 greater the regeneration. The less impeded, the greater the 

 movement of the coenosarc. Whether enough coenosarc is pres- 

 ent or is regenerated, to make up for the recession of the coenosarc 

 will determine whether or no hydranths will appear at the cut 

 end. The basal movement brings additional coenosarc to the 

 basal end, condenses it greatly and thereby increases the number 

 of basal polyps, on small pieces, on lateral branches and on pieces 

 from the distal region of stems. The ccenosarc in the middle and 

 basal parts of the stem does not withdraw from the oral cut end 

 and, as a matter of fact, there are more hydranths at the oral than 

 basal ends. In this hydroid at least, we do not need to call to our aid 

 "formative stuffs,"^- and other hypothetical internal forces and 

 materials to account for heteromorphosis, for the movements of 

 the coenosarc account for the presence or absence of polpys at 

 some levels and not at others. 



The coenosarc of stems kept long in the aquarium often becomes 

 fragmented. Fragmentation is the result of a splitting of the 

 coenosarc at one or another of the internodes; the coenosarc thins 

 rapidly at these points, and finally breaks into pieces entirely 

 independent of each other. Each part may move into the nearest 

 lateral branch and give rise to polyps, or it may remain in the stem. 

 Not infrequently in the latter case it contracts at both ends ulti- 

 mately forming an ellipsoidal dense mass of coenosarc near the 

 basal end of the stem. It is believed that these hydroids winter 

 over in this contracted condition. When stems are subjected for 

 a long time to adverse conditions the coenosarc forms this dense 

 ellipsoidal mass. When such stems, which could no longer be 

 made to regenerate, were cut into smaller pieces, polyps regen- 

 erated provided the coenosarc was injured. 



With a low power of the microscope the lumen within the coeno- 

 sarc is seen to be filled with a colorless fluid in which myriads of 

 colorless granules float. These move slowly toward one end of 



'^The hypothesis of specific stuffs, moving in definite directions, was developed by Bonnet, later 

 by Sachs, and still further perfected by Locb. For criticism, see Morgan 'oi Archiv f. Ent., Bd. ii, 

 '02 ibid., '04 Journ. Exp. Zool. 



