MEGAZOOIDAL INDIVIDUALS 



93 



separate sporosacs a new type clearly evolved in which the 

 successive sporosacs on a sexual branch suffered sufficient 

 terminal compression during their development to form 

 what is known as a " gonoblastidium," or a spray of sporosacs 

 arising close to each other from a sexual stem, and enclosed 

 in a capsule. This, in reality a manifestation of the intensi- 

 fication of Continuity, is the form of sexual apparatus borne 

 by certain Hydrozoa of the present time, and is diagram- 

 matically represented in the next figure. 



Fig. 28. — Diagram of the aporosac-gonoblaatidium of the 

 Hydrozoal colony. 



But terminal compression had still further work to do, 

 and by acting on some primitive sporosac -gonoblastidium 

 (as this developed) it produced the medusiform gonophore. 



Elongation of the gonoblastidium stem bearing the 

 sporosacs was not allowed to take place, but serial and 

 lateral compression treated the whole system, as it tried 

 to develop, roughly in the same way as they did the vege- 

 tative zooidal system which became the primitive sea- 

 anemone. In the case of the early sea-anemone a whole 

 potential Individual system was compressed, whereas in the 

 medusiform gonophore only a small part of one was so 

 affected ; but the real difference between the two cases is 

 that in the former tubular vegetative zooids were involved, 

 and in the latter sexual zooids of sporosac form. 



