304 ERNEST WAEREN. 



tliecEe on the main stem between every two pairs of pinnjB ; 

 but sometimes there are only two pairs, and occasionally only 

 a single pair (text-fig. 7,£). 



Diameter of main stem just below the proximal pair of 

 pinna3, 0"24 mm. ; thickness of perisarc, 40 h- 



The specimen shown in text-fig. 7, C is peculiar, in that a 

 young pinnate shoot is seen springing from the upper surface 

 of the main stem of an old pinnate shoot (o.-s-.). 



Hydrothec a? .—Opposite on main stem, subalternate on 

 the pinna?, usually one pair on every internode. Tubular in 

 shape, expanding upwards ; aperture oval with four outer 

 marginal teeth alternating with four inner {cf. figs. 23 and 24, 

 PL XLYI). In a vertical section (fig. 25) through the hydro- 

 theca three projecting thickenings of chitin may be seen, one 

 in the middle of the inner surface (?•.), one near the margin 

 of the outer surface {x>lt.), and a curved peg (/.p.) near the 

 base on the outer surface. 



Length of hydrotheca 0'38 mm., and greatest breadth 

 0-18 mm. 



Bale ^ mentions and figures an oblique fold (inti'a-thecal 

 ridge) extending across the hydrotheca from the process (r.) 

 on the inner surface. In the Natal hydroid this fold is scarcely 

 represented. 



Hydrantli. — Short conical hypostome and a verticil of 

 23 tentacles (fig. 25). There is the usual dilatation of 

 the coelenteron on the outer side [CD.), and in the con- 

 tracted condition of the polyp there is also an expansion on 

 the inner side [i.p.). The outer dilatation is attached to the 

 peg of perisarc at the base of the outer surface (Z.jJ.) ; the 

 endodermal epithelium on the outer side is flat and undifferen- 

 tiated {u.e.]. The rest of the endoderm consists of elongated 

 cells with granular cells wedged between. The inner surface 

 of the hydrotheca is lined by a thin layer of ectoderm {*'.■'<.) 

 which joins the ectoderm of the polyp at the extreme base. 

 At the front outer edge of the hydrotheca there is a concave 



' Bale. W. M., ' Catalogue of the Australian Hydroid Zoophytes,' 



]884, p. 85. 



