336 ^fi'^ Philippine Journal of Science ma 



tentacles is fairly uniform — 1.2-1.5 mm. — ^the difference in length 

 of the hydranths being mainly due to variation in the region below 

 the tentacle zone. At the base of the hydranth there is a groove 

 separating two regions of very large ectoderm cells, the whole 

 corresponding to the sense ring of Weismann ('81), Congdon 

 ('06) , and others. The large ectoderm cells just distal to the ring 

 contain a considerable number of large, irregularly placed 

 nematocysts. 



The trumpet-shaped hypostome is slender and small in propor- 

 tion to the size of the hydranth, measuring, when extended, 

 about 0.35 mm. in height and 0.18 mm. in diameter at the widest 

 part which is near the distal extremity. When expanded, it is 

 very short and broad with a wide aperture and everted lips. 

 Because of the small size of the hypostome, the large number 

 of tentacles, and their being distally directed, the hypostome is 

 only rarely to be seen in uncleared specimens. 



Under the low power of the microscope the tentacles have a 

 very rough appearance due to the irregularity of the ectoderm 

 and to the presence, especially in their distal portions, of nu- 

 merous small nettling cells in groups of 2 or 3. 



The female gonophores are carried in a verticil of from 4 to 

 6 just above the sense ring on the shortened, and oftentimes 

 partially atrophied, female hydranths. Each gonophore is in 

 the form of a circular tube of endoderm, continuous with the 

 endoderm of the hydranth, having the ovum in its crook, the 

 whole surrounded by a layer of ectodermal cells continuous 

 with the hydranth ectoderm. They measure when mature about 

 0.5 mm. in height, 0.5 mm. in breadth, and about 0.25 mm. in 

 thickness. In many cases the endodermal tube relaxes and 

 allows the ovum, encased in mesoglcea, to hang down beside the 

 pedicel, to the perisarc of which it becomes attached, and where 

 it remains after the tube and, in the majority of cases, the 

 hydranth have entirely disappeared. 



The male gonophores are also borne on the hydranths, usually 

 2 to a hydranth. I have noticed several cases where only 1 

 gonophore was produced and a few in which there were 3, but 

 in far the greater number of cases there are 2 gonophores de- 

 veloped on opposite sides of the hydranth near the tentacle zone. 

 They are paddle shaped and 2- or 3-chambered, measuring in 

 length about 0.6 mm., in breadth about 0.4 mm., and in thick- 

 ness about 0.3 mm., and are often longitudinally divided at their 

 outer extremities. The shortest axis of the gonophore is in the 

 line of the greatest axis of the hydranth. 



