ON THE BRITISH ANNELIDA. 249 



vessels. But such is not the conclusion to which the careful practical observer 

 is conducted by the study of the actual phsenomena of the process. It is of 

 course indisputable that nature accomplishes some adequate object by the 

 fission of the body of the worm ; but that object, whatever else it be, is un- 

 questionably not that of multiplying the species. The tail-fragment never, 

 as can be proved by easy observation, produces a single new ring or segment 

 of the body. If this be true, how completely improbable must be the state- 

 ment that the headless piece is capable of reconstructing a new headl In 

 Arenicola and Nais the author can confidently declare that such reproduc- 

 tive properties as those implied in the reformation, and that too by a remnant 

 of an integral part of the body, do not exist. It is equally inaccurate to 

 maintain that a new tail is formed by the cephalic fragment. This half of 

 the divided worm, like the former, gradually presents evidences of decay ; it 

 becomes less and less irritable, the muscles and integuments begin to decom- 

 pose, the blood-vessels of the branchiae become blacii, and the whole disap- 

 pears by the dissolution of the structures. 



If, as is commonly affirmed by zootomists, each individual ring of the body 

 constituted a real organic submultiple of the entire animal, the possibility of 

 its iadependent existence could be readily conceived. This however is not 

 the case. In Arenicola, Nais and Terebella, and many other species, the 

 reproductive organs are limited to the anterior two-thirds of the body. They 

 do not exist in the caudal segment. When this latter part therefore is de- 

 tached from the cephalic extremity, it is evident that it cannot be regarded 

 as a totuyn irdegrum, a perfect animal in miniature. It wants the most im- 

 portant and essential components of a perfect organism — the generative ap- 

 paratus, without which the mind cannot realise the conception of distinct 

 individuality. In Nais Jiliformis the division most frequently happens at a 

 short distance from the head, through the very middle of the glandular mass 

 of the reproductive organs, tubes being cut across, and the testicular glands 

 being bisected. These extraordinary facts, correctly interpreted, prove clearly 

 that there can be no method in this spontaneous fission of the body, no one 

 situation selected in preference to another, no including of one system of 

 organs and an excluding of another, no definite intelligible ruling principle. 

 What then can be the meaning of such an extraordinary freak of nature? 

 Is it an accident which befalls only a few luckless individuals ? The sand of 

 the sea-shore and the mud of the freshwater pools are thickly strewn with 

 the mutilated bodies of these worms, the former situation of the Lug, and 

 the latter of the Naiades. It is a catastrophe, in which every autumn in- 

 volves the whole community. 



The following interpretation of the above facts, the truth of which cannot 

 be disputed, may be presented as best accordant with what is at present 

 known with reference to the history of the reproductive process in these 

 worms : — 



1st. These Annelids are annuals ; the term of existence is completed when 

 the organic cycle is once accomplished. They are born during the latter 

 months of one summer, and survive the winter, attain to the maturity of 

 growth, reproduce the species, and die by the spontaneous subdivision of the 

 body into fragments on the arrival of the same season of the succeeding year. 

 This brief round comprehends the history of each individual. Since these 

 worms are monoecious, each shai-es the common fate. Each contributes by 

 its own death to the multiplication of the species ; the species being multi- 

 plied, the ends of its own existence are accomplished. 



2nd. For some time before the fission of the body occurs, the process of 

 the maturation of the ova is proceeding. Arrived at the matured phase, they 



