136 A NEW FAMILY OF HYDROIDEA. 



(c) Reproductive structures. 



The only specimen bearing reproductive structures was a male colony. The 

 gonothecas (Figs. 18, 19, 23) are simple and pear-shaped, with a large terminal 

 opening and short stalk springing from the axil of a pinnule. Each contains one 

 gonophore (Fig. 18), which in longitudinal section is seen to arise from the 

 blastostyle and to fill nearly the whole cavity. The blastostyle in the spirit- 

 preserved specimen examined was much shrunken with a terminal swelling (D) below 

 the opening of the gonotheca. The cell-layers could not be distinguished. The two 

 prominent parts of the gouophore are the mass of sperm cells (sp), which stain deeply, 

 and the spadix (Fig. 19, end.) Outside the sperm cells a very thin layer of ectoderm 

 can be distinguished. I failed after long searching to recognise any trace of 

 reproductive elements in the coenosarcal tubes or blastostyle, or any appearance of 

 the formation of more than one gonophore in each gonothecse, though in 

 P. echinulata Weismann states that very often a second gonophore may be found 

 before the contents of the first have passed out.* In P. halecioides also it seems 

 that two may be present at the same time.f 



* Entstehung der Sexualzellen bei den Hydromedusen, p. 180. 

 t Loc. cit., p. 184. 



