CA.MPANLLAKIAN HYDROID. 51 



edofes of the mouth are entire, without lobes or oral ten- 

 tacles, in the younofer specimen, but divided into four oral 

 lobes in older ones. 



2. The radiating ch^Tiiiferous tubes, which may be traced 

 fi'om the base of the manubrium for a short distance to- 

 wards the free edge of the umbrella. 



3. The flattened discoidtd inverted umbrella. 



4. The marginal tentacles. These vary in number, ac- 

 cording to the species, but they are always aiTanged equi- 

 distantly around the entire circumference of the umbrella. 

 There is always one, which may l>e called the radial ten- 

 tacle (Fig. 15, 7^, 1) in the plane of each chymiferous 

 tube, and another, which may be called the median inter- 

 radial tentacle (Fig. 15, F^ 2) midway between each two 

 radial tentacles. In the species figured there are always 

 two, and occasionally three between each radial tentacle 

 and the nearest median tentacle. 



5. The otocysts. Eight small transparent spherical 

 vesicles, situated upon the oral faces of the bases of the 

 eight tentacles adjacent to the four median tentacles. 



6. Examine larger specimens, which may usually be 

 o])tained in abundance by dipping at the surface of the 

 ocean on calm evenings, and notice : — 



a. The very numerous marginal tentacles. 



5. The four deepl}' cleft oral lobes. 



c. The four rounded reproductive organs which project, 

 beyond the outline of the sub-umbrella, one near the mid- 

 dle of each radiating chymiferous tube. 



III. Kill a specimen with osmic acid, as directed in 

 Section VII., and after staining with picro-camiine, mount 

 it in dilute glycerine, and examine it with a high power — 

 two hundred to five hundred diameters — and notice : — 



a. The ab-oral surface. 



