10 



A. DEHISCENCE - 



The e.-^gs are embedded in the ectodenmal tissue 

 of the gonad as in a gelatinous matrix. The round thicken- 

 ed edge of the ribbon contains the riper eggs, but the thin- 

 ner portion is v/ell packed with maturing ova. Dehiscence 

 takes place by the breaking down of the superficial ecto- 

 dermal investment and the liberation of the eggs and sper- 

 matozoa imbedded in its substance. The contractions of the 

 umbrella in swimming piit a strain upon the subumbral walls 

 and help to rupture the epithelium of the gonads, V/hat the 

 cytological change is which precedes the extrusion of the 

 sexual elements or the nature of the causes which effect 

 this change are matters of uncertainty. We know only that 

 these conditions can be artificially induced by means to be 

 mentioned presently. 



The process of dehiscence occupies only a very few 

 moments. Host of the eggs which are ready for fertiliza- 

 tion are extruded all at once, coming out of the bell-cav- 

 ity in a cloud at each contraction of the marginal ring. 

 Two or three minutes after the first eggs are extruded only 

 a few belated ones are loosened from the gonads and expell- 

 ed from the subumbral cavity two or three at a time. Fig- 

 ure 3, is drawn from a sketch made of a medusa in the act 



