148 Transactions. 



The medusa buds are shortly stalked, and the stalk contains a stomo- 

 chord. There are four very short, blunt tentacles, one opposite the end 

 of each radial canal. The medusa bud (fig. 5) is campanulate. The manu- 

 brium is pear-shaped, with the mouth at the narrow end. Scattered 

 sparingly are enormous nematocysts, which are seen in section to project 

 downwards into the mesogloea (fig. 6). Cross-section shows on the surface 

 of the ex-umbrella four interradial grooves. In the detached specimen men- 

 tioned above small bodies are developing on the margin of the bell opposite 

 the ends of these grooves. These bodies will probably prove to be statocysts. 



The ectoderm of the ex-umbrella consists of flattened cells. At the 

 extremity of the tentacles these give place to columnar cells, many of which 

 are nematoblasts. The inner ends of these cells are dark with granules, 

 but are not pigmented. There is probably no reason to regard these ex- 

 tremities of the tentacles as ocelli. Longitudinal section shows that the 

 tentacle contains a central mass of cells that look much like nerve-cells ; 

 but these are cut off from the ectoderm by mesogloea. They are large 

 vacuolated cells of the endoderm, with well-developed nuclei. The nuclei 

 are surrounded by an envelope of protoplasm, from which envelope strands 

 cross the vacuole to the opposite wall. The mass is in direct continuation 

 with the endoderm that lines the radial canal, and is a specialized portion 

 of the endoderm lamella. It is possible that the condition of these cells 

 is preparatory to the hollow state of the tentacles that characterizes the 

 Clavidae ; but if a hollow were to be developed on lines at present suggested 

 by the appearance of the section the result would be a hollow lined by 

 mesogloea, which is not at all likely to occur. Longitudinal section taken 

 between the radials shows no circular canal, which probably develops later. 



The ectoderm of the sub-umbrella consists of columnar cells, differing in 

 length. The result is an epithelium somewhat resembling in appearance 

 the endoderm of the gastro- vascular cavity of the hydranth. The ectoderm 

 cells about the mouth and the lower portion of the manubrium are columnar 

 cells of great size, many of them nematoblasts. 



None of the specimens sectioned show gonads, and it may be presumed 

 that they are immature. 



Ascidioclava para silica is found in the peripharyngeal groove of an 

 Ascidian (a species of Polycarpa) that occurs below low-water mark in 

 Wellington Harbour. It, or an allied form, occurs sometimes, at all events, 

 in the stalked Ascidian Boltenia pachydermatina. It is sometimes present 

 in such abundance as almost to fill the peripharyngeal groove of the host. 

 Attachment is very slight. I have frequently found small masses or de- 

 tached portions in the pharynx of the host or in the stomach ; but these 

 were always dead and more or less macerated, or partially digested. 



The infrequency of parasitism among the members of the class adds to 

 the interest of this form. 



All drawings made with Abbe apparatus. 



EXPLANATION OF PLATE I. 



Fig. 1. Ascidioclava parasitica, enlarged. 



Fig. 2. Section of body-wall of hydranth. gl., gland-cell of endoderm. 



Fig. 3. Section of body-wall of lower part of hydranth and upper part of hydrocaulus. 



Fig. 4. Section of base of hydrocaulus and adjacent portion of coenosarc. end., endo- 

 derm ; m., mesogloea ; ect., ectoderm. 



Fig. 5. Medusa buds. 



Fig. 6. Section of tentacle and part of umbrella, m., mesogloea ; nb., nematoblast : 

 v., velum ; ex.n., cx-umbral nerve ring ; r.c, radial canal. 



