ASEXUAL REPRODUCTION, 



195 



(sea-anemones and corals), which lead to a passive terminus again, and 

 exhibit profuse asexual multiplication. A few sea-anemones divide 

 normally, just as they may be multiplied by artificial cutting. Fragments 

 may also be given off in an arbitrary sort of fashion, reminding one of the 

 overflow buds of sponges. The division may be either longitudinal or 

 crosswise in sea-anemones, and the budding of corals takes many forms, 

 resulting in the quaint complexity of brain-corals and the like. In one sea- 

 anemone {Gonactinia prolifera)^ where transverse division occurs, it is 

 interesting to notice that this has only been observed in young forms with 

 undeveloped sexual organs. It recalled, in fact, the asexual multipliaticon 

 of a young jelly-fish. In another of the corals 

 {Antipatharia) Brook has recently observed how a 

 nutritive "person" may by constriction form a re- 

 productive individual on either side. 



JVor?ns. — The lower worm-types are roughly dis- 

 tinguishable from most of the higher by the broad fact 

 that they are all of a piece, without rings or segments. 

 A physiological link, however, between worms of only 

 one segment and those with many, is found in the 

 asexual chains which some of the former occasionally 

 develop. Thus the little turbellarian Microstomu7)i 

 lineare may bud off a temporary chain of sixteen in- 

 dividual links. The budding begins at the posterior 

 end, and what is partly separated off is a portion in 

 excess of the normal size. The second link grows 

 till it attains the usual adult size, and as it exceeds 

 this form a third link. At the same time the original 

 individual may also be doing the same, and thus a 

 chain of four is formed. Two more buddings by each 

 of the links bring the asexual process to a climax, and 

 then the individuals separate from one another and 

 become sexual in freedom. It is important to notice 

 that the asexual reproduction takes place in favourable 

 nutritive conditions, and as each individual exceeds 

 its normal limit of growth. In some allied planarians 

 the asexual multiplication is effected not by budding 

 but by division. Zacharias observed, that when nutri- 

 tion was checked the vegetative increase ceased, and 

 sexual reproduction set in. Not quite parallel with the 

 above, but quite asexual, is the prolific multiplication 

 characteristic of the flukes and tapeworms. The 

 common liver-fluke has often several asexual generations before it finds its 

 final host in the sheep, and is surpassed in this respect by some of its 

 relatives. The bladder- worm, in passive ease, with a plethora of nutrition, 

 may form asexually many "heads," each of which, inside a future host, 

 grows out into the long series of joints which compose the tapeworm. In 

 their profuse asexual multiplication these parasites are like parasitic fungi, 

 but unlike them in the retention of the sexual process to boot. 



In their asexual reproduction, the Polyzoa recall sponges, for not only 

 do they all multiply by budding, and that abundantly, but they form 

 peculiar winter-buds like sponge-gemmules, by which on the death of the 

 parent the continuity of life is nevertheless sustained. The winter-buds or 



Diagrammatic repre- 

 sentation of the for- 

 mation of a chain 

 of individuals in the 

 Turbellarian worm 

 Microstomujn lin- 

 eare. — From I.eu- 

 nis. 



