284 R- E. Llovd : A new genus of Hydroids. [VOL. I, 



Considerable difficulty was experienced in interpreting the 

 structure of the basal plate, for although the histological detail was 

 fairly well preserved, there was little or no difference in the ap- 

 pearance of the endodermal and ectodermal layers ; both varied 

 in thickness, to a great extent, in different parts. Figure 5 (pi. 

 xvii), which was drawn with the camera lucida from a favour- 

 able section, shows the principal features in the structure of the 

 coenosarc. It will be noticed that the cuticle is relatively very 

 thin, in some parts of the colony it is hardly recognisable. 



GonopJiores — 



The colony shows both male and female gonophores. With 

 hardly an exception, one gonophore is situated at the base of each 

 hydranth. Careful examination shows, however, that the endoder- 

 mal layers of the gonophores are not directly connected with the 

 endodermal canal at the base of the hydranth, but spring from 

 the irregular endodermal spaces of the neighbouring coenosarc. 

 This is shown in pi. xvi, fig. 4. The gonophores are of the closed 

 type known as sporosacs. They show no traces of tentacles, radial 

 canals or ectodermal invagination. 



The female gonophore was only studied in optical section, but 

 as its structure was much simpler than that of the male ones, a 

 comprehensible plan of the structure can be made out after study 

 by this means alone. Figure 5 shows the principal features of the 

 structure of these organs. They are spherical bodies, measuring 

 ■17 mm. in diameter, and are each attached to the coenosarc near 

 the base of a hydranth. Their endodermal contents, which arise 

 from the coenosarc and not from the special endodermal canal of the 

 neighbouring hydranth, split into two layers on entering the gono- 

 phore. The outer of these layers forms an uninterrupted sheet, 

 closely applied to the ectoderm ; the inner forms a spadix of 

 characteristic shape. This spadix, the walls of which are, by in- 

 vagination, composed of a double layer of endoderm, forms a glo- 

 bular body separated by a considerable space from the wall of the 

 sporosac. There is an opening in one side of the spadix due to the 

 invagination, so that in longitudinal sections it forms a character- 

 istic C-shaped figure. Developing ova can be seen between the 

 layers of the spadix : in at least two cases ova of larger size than 

 the others can be clearly seen in the canal of the neck of the 

 spadix. Perhaps this is a preliminary position before the ovum 

 passes into the central cup-like hollow. When the surface of a 

 large ovum is examined under a high power of the microscope, it 

 shows a delicate hexagonal pattern, caused by the approximated 

 ends of the long columnar cells of the spadix pressing on it. Ova 

 more advanced than the one shown in fig. 5 were not found. 



The male Gonophores — 



While the part of the colony seen in fig. 3 showed female 

 gonophores chiefly, other parts showed the male form. This is of 

 about the same size as the female gonophore, but is shaped like a 



