,88 ERNEST WARREN. 



the growing gonangium. Subsequently the genital cells will 

 separate themselves from the endoderm on one side of the 

 blastostyle, and this may be regarded as representing the 

 formation of a gonophore (fig. B, t), which is covered by a 

 thin layer of ectoderm cells continuous with the ectoderm of 

 the blastostyle. At the apical region the ectoderm (c.^J.) 

 of the blastostyle consists of elongated cells constituting the 

 " Deckenplatte " of Weismann. 



Female Gonangium. — The gonotheca when mature is 

 ovoid and flattened. The plane of flattening is at right 

 angles to the antero-posterior plane passing through the 

 main-axis. 



The female gonotheca arises on the main-stem just below 

 the hydrotheca and on one side of the sub-calycine nemato- 

 phore. It possesses a short stalk-segment with transverse 

 nodes (text-fig. 1, C, n..^, n...). The stalk and the basal 

 portion of the gonotheca are so curved that the main-axis of 

 the structure is set at an angle of about 30° to the main-stem 

 (text-fig. 1, C and D). The oldest gonangium is the most 

 proximal one, and the gonangia are successively younger on 

 passing distally. The perisarc is not ver}^ thick, but there is a 

 well-defined large opercultmi^ and there the perisarc is stouter. 

 At the base of the gonotheca itself and on the flattened 

 surface there is a neraatophore on each side (text-tig. 1, D). 



Length about 0*81 mm., greatest lateral width 0"51 mm., 

 thickness at right angles to plane of flattening 0*r2 mm. 



The female gonangium bears in an obscure manner a 

 single gonophore which becomes provided with a single 

 ovum. Before the ovum commences segmentation the gono- 

 theca is very hollow, and the blastostyle occurs as a thin 

 tubular structure running through the mid-axis. 



Systematic Position.^ — The hydroid possesses the typi- 

 cal characters of the genus Plumularia with the 

 exception of the presence of the downwardly directed off- 

 shoots from the pinnge, and the somewhat unusual occurrence 

 of the main-stem bearing hydrothecje. These pinnules are 

 similar in every way to the pinna?, and they originate from 



