242 THE EVOLUTION OF CONTINUITY 



alternation as in I, but as there is filamentous Continuity, 

 and as a result, temporary cell-arrest, the phenomenon is 

 more clearly observable ; a given filament displaying at 

 the same time sexless intermediate cells and sexual cells 

 or gametes (Fig. 80). 



III. The Ccenocytic Individual. — In this no less than three 

 forms of the alternation may be offered, (a) Protoplastic ; 

 there being protoplasts which, arrested on the road to 

 become sexual, contrast with forms which as gametes are 

 sexual. (6) Ccenocytic ; whole sections of mycelium con- 

 taining sexless protoplasts contrast with sections which, as 

 gametangia, contain gametes, (c) Mycelial ; as where an 



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^V^-Iamifanffo,,, 



«V 



Fio. 81. — a, Protoplastic and Coenocytic alternation of cycle- 

 stages ; the protoplasts alternating with the gametes, and the 

 coenocyte with the gametangium. b, Mycelial alternation, 

 the mycelium bearing spores alternating with that producing 



original mycelium produces only spores, and the mycelia 

 arising from these produce gametes. 



IV. The Discontinuously Zooidal Individual. — In such 

 (e.g. Hydra), there is the alternation of the sexless body-cell 

 with the sexual element. But in addition there is zooidal 

 alternation. But as the zooids are discontinuous, the sexless 

 condition is temporary. It is the alternation of the dis- 

 continuously multicellular Individual in a higher form 

 (Fig. 82). 



V. The Continuously Zooidal Individual. — Here also the 

 alternation is cellular and zooidal ; but as many zooids 

 are permanently arrested owing to Continuity, and adapta- 

 tion to special function, the sexless and reproductive zooids 

 form a striking and enduring contrast, heightened by the 



