A COLLECTION OF HYDE01D8. 293 



side (PI. XL VII, figs. 18 and 19 Aj) and one below the abcau- 

 line tooth (A'o). Sometimes there are four knobs, the abcauline 

 one being" replaced by two in the middle of the abcauline 

 sides of the square. There is an operculum of four flaps. 



Length of hydrotheca, measured parallel to the abcauline 

 surface, 0"55 mm ; greatest breadth, 0'26 mm. 



Hydra nth. — It has the typical sertularian structure with 

 the dilatation of the coclenteron on the outer side, and a sheet 

 of ectoderm lining the upper portion of the inside of the 

 hydrotheca. The hypostome is conical, and there is a verticil 

 of about 25 tentacles. The nematocysts on the tentacles 

 are small and narrow ; they measure about 6*2 fx in length 

 and 1'8 ij. in breadth. 



CtOnosome. — The gonangia are produced from the hydro- 

 caulus just below a hydrotheca ; they are provided with three 

 apical teeth. The male differs from the female in being 

 narrower, and the apical teeth tend to be longer and closer 

 together. The male gonangium (text-fig. 5, ^4) has 3 or 4 

 rings around the apical region, while it is smooth below : the 

 female (B) has 5 or 6 rings. 



The male gonangium has an average length of 2"28 mm. 

 and greatest breadth 0"73 mm. The female measures 2'42 

 mm. and 0*97 mm. respectively. I'hickness of perisarc 

 about 17 /(. 



Sometimes short lateral branches (PI. XLYII, fig. 19, h) 

 arise from the inside of a hydrotheca, thus recalling the mode 

 of origin of the gonangia in the genus Synthecium, In 

 one case a single hydrotheca, complete with operculum, issued 

 from the old hydrotheca; this was doubtless formed after the 

 disintegration of the polyp and during its subsequent renewal. 



Gall caused by a Pycnogonum. 



Occasionally there may be seen springing from the inside 

 of a hydrotheca a large fusiform body. This structure, which 

 may be three times the length of a hydrotheca, is a gall 



