24 Dr. F. von Wagner on 



the parent, and has its alimentary canal in common with it, 

 as in the case of the old and young Hydra before separation 

 has taken place. 



In the last (1882) edition of his ' Vergleichende Anatomic' * 

 Schmidt again designates the asexual reproduction of Micro- 

 stoma (as also that of the Naidse) simply as fission. 



In 1849 M. Schultze declared very emphatically that the 

 multiplication of the Microstomids, like that oi Nats, "depends 

 not upon a mere formation of buds, but upon a constriction of 

 a single animal into several, progressing according to perfectly 

 definite laws " f. Like Schmidt, Schultze also herein 

 attached most importance to the fact that " in this there takes 

 place an actual separation of a portion previously belonging 

 to the parent to form a new individual" {loc. cit. p. 294). 



Von Graff, in his ' Neuen Mittheilungen iiber Turbellarien ' 

 (1875), in which we find the first exact description of the 

 asexual reproduction of Microstoma, regards the process as 

 fission, without making any further observations on the pointj. 



Von Graff's results were supplemented, in some cases 

 rectified, by the important investigations of P. Hallez, in 

 particular by the discovery that it is always the posterior 

 third of the body of the multiplying animal which represents 

 the rudiment of the new zooid §. 



Von Graff was subsequently able to confirm this discovery, 

 but it induced him, in his great Monograph of 1882, to 

 declare the multiplication of Microstomids to be a case of 

 gemmation. The following sentences || convey the essence of 

 his view : — " The .... asexual reproduction of Microstoma 

 lineare is undoubtedly to be regarded as gemraatiouj and 

 indeed as a terminal formation of buds, in which tlie posterior 

 end of the parent ' grows and separates itself off as a young 

 individual from the old,' " so that therefore " ' the younger 

 terminal bud ' " is " * subordinate to the older parent indi- 

 vidual.' " 



" It was not until Hallez discovered the fact that it is 

 always only the posterior third or fourth of the parent, there- 

 fore that portion which we may as it were regard as the 



* O. Schmidt, 'Handbuch der vergleiclienden Anatomie,' 8 Aufl., 

 Jena, 1882, p. 107. 



t M. Schultze, " Ueber die Fortpiianzung durch Theiluug bei Nais 

 proboscidea,'" Avch. f. Naturgesch. 15 Jahrg. Bd. i. p. 294. 



X L. Graft", " Neue Mittheilungen iiber Turbellarien," Zeitschr. f. wiss. 

 Zool. Bd. 25, pp. 409 et sqq. 



§ P. Hallez, 'Contributions a I'histoire naturelle des Turbellari^s,' 

 Lille, 1879, pp. 153 et sqq. 



II L. V. Graft; ' Monographie der Tm-bellarien.— I. llhabdoccelida,' 

 Leipzig, 1882, p. 174. 



