HALOCORDYLE COOPEKI. 75 



ties, and over the secondary branches bearing- the polyps 

 it is very transparent and thin. 



Polyj:) is flask-shaped; its average height from base to 

 summit is 0'844 mm. The endoderni of the swollen basal 

 portion is red in the living condition. There are two kinds 

 of tentacles : 



(1) A single whorl of basal filiform tentacles; the typical 

 number appears to be eighty although there may be nine 

 or ten. 



(2) Typically there appear to be two whorls or verticils 

 of capitate tentacles, with four in each whorl ; but there is 

 variation in this arrangement. The tentacles of the two whorls 

 are arranged alternatel}', and they are inserted on the sides 

 of the hypostome. The swollen extremities of the capitate 

 tentacles are provided with very large nematocysts, {)"0387 mm, 

 in length and 0'017 mm. in breadtli ; while the filiform tentacles 

 and the general ectoderm oi the polyp have nematocysts, 

 about 0"0112 mm. in length and 0"0054 mm. in breadth, but 

 they are far more variable in size than the large nematocysts, 

 and perhaps there are several kinds. 



In Pennaria cavolinii Ehren. Allma:i describes the 

 filiform tentacles as being slightly swollen at their extremities; 

 such does not appear to be always the case in H. coojDeri. 



In the fully expanded condition the mouth is large and 

 funnel-shaped. 



(2) Histology. — Ectoderm : The ectoderm is of the usual 

 type, and contains, as we have seen, two kinds of nematocysts. 

 The nematocysts appear to be confined to the ectoderm, as I 

 have been unable to find any in the endoderm ; although in 

 the hydroid f^ibularia solitaria, which is also described 

 in this journal, nematocysts are exceedingly abundant in the 

 inner layer. 



The large nematocyets are mostly confined to the swollen 

 extremities of the capitate tentacles (fig. 6, l.n.), although I 

 have occasionally found them in the ectoderm of the coenosarc. 

 '^Phe small nematoc3'sts occur on the capitate tentacles and 

 generally throughout the ectoderm. 



