CAMPAXLTLARIAN HYDROID. 49 



3. The supporting layer (Fig. 25, 3) separates the 

 endoderin fi-om the ectoderm in the manubrium and in the 

 tentacles, and it also runs out between the two epithelial 

 surfaces of the velum. 



Vni. THE MEDUSA STAGE OF A CAMPANULA- 

 RIAN HYDROID. 



I. ExA^rnsTE specimens of the hydroid which was de- 

 scribed in Section VI. , until one is found which has repro- 

 ductive calycles (Fig. 15, JB and C). These will usually 

 be found near the bottom of the hydi'ocaulus. Having 

 found a specimen, cut off the section of the stem which 

 carries the reproductive calycles, and place it upon a slide 

 under a cover glass, in a drop of sea-water, for microscopic 

 examination. Examining it with a low power, fifty to one 

 hundred diameters, notice : — 



a. The gonangium, or capsule of perisarc (Fig. 15, d) 

 which corresponds in general outline and in its position 

 upon the stem, to the hydrotheca of one of the ordinary 

 nutritive hydranths, although it is longer, and is closed at 

 its free end. 



b. The blastostyJe, or rudimentary hydi-anth (Fig. 15, c) . 

 This consists of a long slender stem or axis, which cor- 

 responds to the body of one of the nutritive hydranths ; 

 and a club-shaped tip, or manubrium, with scattered 

 nematocysts. 



There are no tentacles, and the manubrium has no ter- 

 minal orifice or mouth ; but the body layers which have 

 been examined in the hydranth may be seen in the blasto- 

 style, and there is a central ciliated body-cavity, continu- 

 ous with the cavity of the hydrocaulus. In transparent 

 specimens particles of food may be seen to pass up the 

 stem into the blastostvle. 



