MORPHOLOGY AND DEVELOPMENT OF EUDENDRIUM. 37 



The function of the upper ring of thread cells is probably pro- 

 tective, as we can hardly conceive of any offensive use in this 

 place. The object of the glandular tissue of the two rings as 

 well as of the groove seems obscure. The occurrence of rings 

 without cnidophores goes to confirm Weismann's statement that 

 cnidophores and rings have independent functions. 



Pedicel and Stem. There is little unusual in the histology of 

 the pedicel and stem. The narrow neck connecting hydranth 

 and pedicel consists of typical cambium tissue as described by 

 Jickeli, '82 ; Seeliger, '94, and others. The enteric cavity is 

 much constricted. The entoderm consists of brightly staining 

 cells which appear in more vigorous condition than much of the 

 tissue below them. The cell borders are well marked. Active 

 gland cells occur here and there. 



The ectoderm of the ccenosarc is first affected by degenerative 

 changes of all the tissues of the colony. Large masses of thread 

 cells occur in it, when thus affected, and they are in all stages of 

 development. The youngest appear as small refractile bodies in 

 cells full of deeply staining granular cytoplasm. As they grow 

 larger a deeply staining rod appears in the axis of the body. It 

 develops into a loop, and then into a coil of about ten loops. At 

 this stage the membrane of the parent cell is filled by the struc- 

 ture and the shrunken nucleus is crowded between it and the 

 membrane. 



Weismann, 'Si 2 , described slow peristaltic contractions of the 

 ccenosarcal column of hydroids as well as amoeboid movements 

 of ectodermal processes along the inside of the perisarc. When 

 a cover glass was pressed down over a freshly cut portion of a 

 branch some processes were seen to withdraw from the perisarc 

 and others to reach out to it. I find a condition of the ccenosarc 

 very suggestive of such movements. In most branches the ecto- 

 derm is attached to the perisarc in but few places and is else- 

 where contracted in varying degree. Doubtless a certain amount 

 of contraction also results from the action of the killing fluid. 



Bands of mesogloea sometimes are found extending to the 

 perisarc of pedicels and branches. The ectoderm reaches out 

 and around the band to its point of attachment, thinning to a 

 mere film which passes between it and the perisarc (Fig. /). 



