832 



THETIS SCIENTIFIC RESULTS, 



The hydranths are attached to the hydrotheca some short dis- 

 tance above the free end of tlie internal wall, the level being 



marked by a slight constriction of 

 the hydrotheca. Low prominences 

 set in a ring stud the internal sur- 

 face of the perisarc at this point, 

 and to these a disk of coenosarc at 

 the base of the hydranth is attached. 

 But beneath the attached basal 

 disc, a second attachment occur.'*, for 

 irregular strands of sarcotie l>ranch 

 from the ectoderm imme'liately 

 belovir the hydranth and are attached 

 to the walls of the hydrotheca. A 

 similar development occurs in Lao- 

 medea geiiiculata^ ^ . The hydranths 

 are strongly contractile, and when 

 fully withdrawn form a very short 

 stout cylinder. Expanded, each con- 

 sists of a long narrow cylindrical 

 neck, surmounted by a fusiform 

 " head," which terminates in a 

 small shaiply-conical hypostome. 

 This is surrounded by a circle of 

 sixteen or seventeen tentacles. As 

 to minute structure — The tentacles 

 consist of a moderately thick ecto- 

 derm which contains few nemato- 

 cysts arranged in whorls, and of 

 skeletal endoderm, the septa between 

 the cells of which stretch across the 

 interior of the tentacle. In the 

 body- wall of the hydranth the ectoderm is comparatively 

 thin, and it is lined by a thick endoderm composed of 

 columnar cells which, especially beneath the hypostome, project 

 far into the digestive cavity. Gonosome not present. 

 Dimensions. — 



Fig. 126. 

 Hydranth of Cryptolaria eras- 

 sicaulis var. dimorpha x 70 ; 

 w, external wall of hydrotheca ; 

 ect, ectoderm ; end, endoderm; 

 c, cavity of hydranth ; d, basal 

 disc of attachment ; str, sup- 

 porting strands; b, base of 

 internal wall of hydrotheca. 



Organs. 



Form 1. 

 Adnate specimens. 



Form 2. 

 Free specimens. 



Hydrotheca, length of adnate portion 

 ,, length of free portion.... 



,, diameter at base 



,, ,. ,, mouth 



0-88-1-01 mm. 

 0-70-0-98 ,, 

 0'14-0-18 „ 

 0-38-0 -52 ,, 



1-54-1 -59 mm. 



0-14 mm. 

 0-35-0-40 mm. 



38c, 



See Brooh^Hydroiden : in Fauna Arctica, Jena, v., 1909, p. 183, fig. 



