90 ERNEST WARREN. 



up around it. This thickening of ectoderm will produce the 

 ectoderm -lining to the umbrella cavity and the germinal 

 tissue. 1 have not observed any migTation or wandering of 

 the sexual elements. As we have already seen, male and 

 female gonophores are invariably produced on distinct 

 peduncles, but both kinds of peduncles occur on the same 

 hydranth. In a transverse section of a mature gonophore 

 (fig. 9) we find — (1) the outer ectoderm; (2) two thin layers 

 of endoderm with no development of radial canals; (3) a 

 thin layer of ectoderm, which is the outer ectodermal wall 

 of the umbrella cavity; (4) umbrella cavity, which is mostly 

 occupied by (5), germinal tissue covering (6), manubrium or 

 spadix. 



When the gonophore is mature the um])rella cavity opens to 

 the exterior by a small apical aperture (fig. 19^ o), and it is 

 probable that fertilisation takes place through this opening. 

 No rudiments of umbrella tentacles in the form of processes 

 or knobs are produced. Thus, with the exception of the 

 small aperture to the exterior, the gonophore may be called 

 adeloc.odonic, since no radial canals and no marginal tentacles 

 are formed. 



Among the clumps of gonophores one frequently meets 

 with abortive or semi-abortive specimens (fig. 18). These 

 abortive gonophores appear to be almost invariably the 

 terminal gonophore of the peduncle, although it must be 

 remembered that the terminal gonophore is not always abor- 

 tive. The terminal gonophore of a peduncle differs from the 

 lateral's in (1) the great thickness of the mesoglea, and in this 

 it agrees with that of the peduncle; (2) the great thickness of 

 the outer ectoderm. These two differences can be picked 

 out at once in the sections, and are shown in the comparison 

 of an abortive and normal gonophore in fig. 18. 



An abortive gonophore, male or female, tends to be about 

 one half or two thirds of the size of a normal gonophore. 

 The endoderm of the spadix is relatively larger than in a 

 normal gonophore, and contains swollen nuclei. The umbrella 

 cavity is completely filled with a tissue of small stringy 



