286 ERNEST WARREN. 



hydranth. These stems gradually expand into the hydranth 

 and are only separable from it by reason of the termination 

 of the perisarc (fig. 15, H). 



At times a branch of the hydrorhiza may turn upwards, and 

 its growing apex may develop into a hydranth ; and thus the 

 growth of the branch is terminated. Such has occurred in 

 the specimen shown in text-fig. 3, .4., hij. 



Hydranth. — The general shape is that of an elongated 

 spindle (PI. XL VI, fig. 14). The hypostome region is not 

 sharply distinguished on the outside. Around the mouth 

 there are 4-6 short capitate tentacles ; perhaps four is the 

 typical number. Over the surface of the hydranth there are 

 scattered some 25 moniliform tentacles. The longest of the 

 tentacles are those situated at about one third of the length 

 of the polyp from the mouth ; those at the base are very short. 



The hydranth in the preserved condition may have a length 

 of 3 mm. or more. The diameter of the capitulum of an oral 

 tentacle is 0']33 mm., and the diameter of the terminal swell- 

 ing of a moniliform tentacle may be as much as 0'075 mm. 



GrONOSOME. — Between the moniliform tentacles, and some- 

 what below the middle of the body, short outgrowths are 

 produced, and from these are budded clusters of reproductive 

 bodies. It is probable that they are planoblasts, and ultimately 

 become free (PI. XL VI, fig. 14, jd.) ; since in the most mature 

 of the specimens marginal umbrella-tentacles are fully formed, 

 and the body is practically a medusa, while the sexual elements 

 are exceedingly immature. 



G-eneral histology. — The delicate perisarc of the hydro- 

 caulus dips into a shallow groove of columnar cells at the base 

 of the hydi'anth, and then fades away (PI. XL VI, fig. 15,jj.(/.). 

 The perisarc of the hydrorhiza, separated into distinct layers, 

 is well seen in the figure (_^>.), also in text-fig. 3, B.,iJ. 



The ectoderm is provided with two kinds of nematocysts. 

 The large occur more especially in the capitula of the oral 

 tentacles (fig. 17, l.n.), but they are found also in the general 

 ectoderm of the hydranth and coenosarc; they measure 27"0/u 



