36 EDGAR DAVIDSON CONGDON. 



Tentacle. The few thread cells of the tentacles occur for the 

 most part in the thickened ectodermal tip. There are no exter- 

 nal ridges as in E. ramosiun. The entoderm cells appear polyg- 

 onal in a cross section of the tentacle and form regular transverse 

 layers of uniform thickness. The nuclei are so large as to ap- 

 pear to fill the interior of contracted tentacles. Longitudinal 

 contractile fibers extend along the exterior of the thin meso- 

 glcea. Their distal ends can sometimes be traced out among 

 the ectoderm cells, though I could not demonstrate any connec- 

 tion with them. 



Gland Ring. --Around the base of the hydranth the ectoderm 

 is modified to form the gland ring mentioned previously (Fig. 6) 

 The entoderm does not take any patt in its structure. Weis- 

 mann's description, 'Si 2 , of similar rings refers to E. racenwsmn 

 and E. capillare. He states that it consists of two ridges sur- 

 rounding the base of the hydranth, separated by a narrow groove. 

 The upper one has a varying number of thread cells ; the lower 

 is glandular and may be seen discharging its product which 

 cements together a ring of debris about the base of the hydranth. 



Above the upper ring occurs a muscular organ which Weis- 

 mann terms a cnidophore. It is much like a large tentacle thickly 

 beset with thread cells. The combined structure occurs only 

 occasionally and more often on male than female colonies. He 

 thinks the cnidophore a weapon developed as a protection against 

 some especial enemy. The hydranth of E. hargitti very often 

 possesses a double ring, but I have not found the cnidophore. 

 The degree of development of the ring is extremely variable. At 

 times it is plain to the unaided eye, again not readily detected even 

 with sectioning and staining. Weismann does not describe gland 

 cells in the upper ring. They are plentiful in the Bermuda form 

 wherever it is devoid of thread cells. The distinctly glandular 

 tissue is two or three cells thick and changes gradually into un- 

 modified ectoderm. As noted by Weismann, the length of these 

 cells is considerable, as they extend from the top of the ridges to 

 the mesogloea. Their cytoplasm is deeply staining and granular. 

 The free end swells outward as in other gland cells. Often the 

 upper ring presses down on the other so that the groove opens 

 at a lower level than its interior. The bottom is formed from the 

 extended bases of the gland cells. 



