272 CESTODES. 



in his system beside the polypes among the polyzootic zoophytes, 

 and in other places^ expressly compares it with a plant of many 



shoots. 2 



Linnd's conception was also in advance of his contemporaries in 

 this respect, that hitherto they had been inclined to suppose that the 

 tape-worm arose by the isolated joints (Vermes cucurbitini = chabb al- 

 Jcar'i of the Arabians) subsequently forming a chain. And l^his idea 

 struck its roots so deeply that even Blumenbach, towards the end of 

 last century, regarded it as correct. Even the unequal development 

 of the individual joints, which surely suggests successive budding, did 

 not lead him to alter his opinion. He tried, indeed, to explain it by 

 assuming that the older worms were ever being sucked out by their 

 progeny, and were thus reduced in size. And yet even at this time 

 the observations of Pallas and others had made it almost indubitable 

 that the smaller joints were the younger, and that they attained the 

 larger size as they gradually grew older. 



The conception of the tape- worm as a polyzootic animal could, how- 

 ever, only slowly gain ground. It appeared as though the presence of a 

 distinct and definitely formed head could not be brought into harmony 

 with it. Pallas, following up Linne, had indeed already attempted to 

 regard this head as the root (quasi-radix) of a plant-like animal, yet, 

 with the exception of Eeimarus, but few zoologists supported his 

 idea. And so it has come about that, in spite of the protests of F. S. 

 Leuckart and Eschricht, the tape- worm has even in our own day, in 

 scientific and popular conception, been persistently regarded as a 

 simple animal. 



It persisted in fact till Steenstrup ^ gave us the key to the proper 

 understanding of the tape-worm, by showing its harmony with his 

 theory of alternation of generations, according to which the head was 

 seen to be the larval " nurse," and the joints the sexually mature in- 

 dividuals. The ingenious Danish naturalist left us, indeed, without a 

 strict proof of the correctness of his theory, but this was speedily fur- 

 nished in such masterly fashion by van Beneden* and v. Siebold,'' that 

 it is now hardly permissible to harbour a doubt as to the compound 

 character of these animals. 



^ " Amoenit. acad.," vol. ii., p. 87 et seq. (Dissert, de trenia). 



• Qotting. gelehrt. Anzeig., No. 154, 1774. 



° " Generationsweohsel, " p. 115: Kopenhagen, 1841; " Alternation of Generations," 

 Kay Society, 1845. 



* " Les vers cestoides sontils mono- ou polyzoiques ?" " Vers Cestoides, ' p. 94, and 

 "M6m. sur les vers intest.," p. 251. 



° " Ueber den Generationsweohsel der Oestoden:" Zeitschr. f.wiss. ZooL, Bd. ii.,p. 198, 

 1850. See also his " Abhandlung iiber Band- u. Blasenwurmer," 1854. 



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