XXX PKOOEEDIXaS OF THE 



intestinal canal is a secondary occurrence caused by parasitism, and 

 Haeckel regards them as having descended from worms in which the 

 intestine was present. 



Several years ago Haeckel united into a separate kingdom, under 

 the name of Protista, certain low organisms, some of which had 

 been previously placed among the Protozoa, while others had been 

 assigned to the vegetable kingdom. To this neutral group he refers 

 the Monera, the Flagellatse, the Catallactse, the Labyrinthulese, the 

 Micromycetse, and the Acytariae and Radiolarise. After the elimi- 

 nation of these, there remain as genuine Protozoa, the Amoebinse, 

 the Gregarinse, the Acinetse, and, above all, the true Infusoria or 

 Ciliata. 



The union of the Protista into a distinct kingdom equivalent in 

 systematic value with the animal or vegetable kingdom, can, how- 

 ever, scarcely be maintained. We already know enough of some of 

 them to justify our assigning these to one or other of the two gene- 

 rally accepted organic kingdoms ; and there can be little doubt that 

 did we know the whole Jiistory of tlie others and were able to formu- 

 late the essential difference between the animal and vegetable kingdom, 

 these, too, would be referred without hesitation either to the one or 

 to the other, some passing to the former and others to the latter. 

 The group of the Protista is thus at best but a provisional one, based 

 partly on our ignorance of the structure and life-history of the beings 

 which compose it, and partly on our inability to assign to the ani- 

 mal its essential difference from the plant. Haeckel, however, has 

 done well in specially directing attention to it; and in his admirable 

 researches on many of the organisms which he has thus grouped 

 together, he has largely contributed to our knowledge of living 

 forms. 



I have thus dwelt at considerable length upon this important 

 paper of Haeckel' s, because I think that it not only brings out in a 

 clear light the essential features of infusorial structure and physi- 

 ology as demonstrated by recent research, but that it goes far to set 

 at rest the controversy regarding the unicellularity and multicellu- 

 larity of the Infusoria. 



Balbiani has quite recently published a very interesting account 

 of the remarkable Infusorium long ago described by O. F. Miiller 

 under the name of Vorticella nasuta, and more recently taken by 

 Stein as the type of his genus Didinium. 



The animal, which is somewhat barrel-shaped, with an anterior 



