ANDREW PRITCHARD, \%(i\. H JAMES-CLARK, \^6^. 27 



corresponding with that of Ehrenberg's opus magmun, includes not only 

 the Infusoria proper, but also the several entirely unrelated groups of the 

 Diatomacea^, Desmidiacea^, Confcrvaceae, and many Rhizopods, Radiolaria, 

 and even Acari. It is scarcely to be wondered at that, placed in front of 

 so vast and heterogeneous an assemblage of organic forms, the author 

 should have called in extraneous assistance, and hence it is we find the 

 names of J. T. Arlidge, W. Archer, J. Ralfs, and W. E. Williamson— all 

 high authorities on one or other of the several groups separate from 

 the true Infusoria — associated as coadjutors in the fourth edition of 

 Mr. Pritchard's work. 



Stein's second volume, issued, as already mentioned, in the year 1867, 

 constitutes a monograph of the Heterotrichous order of the Ciliata, and forms 

 a worthy companion to the one previously published, the series of types 

 included in this section being delineated and described with an accuracy and 

 exhaustiveness of detail hitherto unapproached. This monograph embodies, 

 in addition to the above-mentioned more special subject-matter, data of the 

 highest importance concerning the general organization and reproductive 

 phenomena of the Infusoria, and is also notable for containing a formal 

 abandonment, with some slight reservation, of his original theory asso- 

 ciated with the Aciiietce, and acknowledgment of the claim of these animal- 

 cules to the independent position assigned to them by Claparede and 

 Lachmann, This reservation, as above intimated, was manifested by Stein's 

 continued adhesion to the opinion that certain infusorial types, e. g. Stentor, 

 Stylonychia, and Urostyla, commenced their existence within the parent 

 body as minute ovate or subspheroidal embryos, with or without cilia, and 

 possessing in addition a greater or less number of retractile tentaculiform 

 appendages corresponding with those of the ordinary Acinetse. These 

 supposed embryos of the associated Ciliata are, however, now shown to 

 be minute parasites, referable chiefly to Claparede and Lachmann's genus 

 Sphcerophrya. 



The following year (1868) commands a conspicuous position in the 

 bibliography of the present subject, through its association with the dis- 

 covery by Professor H. James-Clark, of the Agricultural College of Penn- 

 sylvania, U.S.A., of certain Flagellate Infusoria exhibiting an entirely new 

 type of structure, accompanied by his simultaneous announcement that all 

 sponges consist essentially of colonial aggregations of similar Flagellate 

 animalcules. Three years later, 1871, the present author had the good 

 fortune to encounter the greater portion of H. James-Clark's types, and 

 several new but closely allied forms, upon this side of the Atlantic, and 

 having since selected this group as the subject of special attention, has so 

 augmented its original numbers and demonstrated their distinctive features 

 as compared with the more ordinary Flagellata, as to have felt justified 

 in establishing for them a new order, upon which it is here proposed to 

 bestow the title of the Choano-Flagellata. Pursuing the path indicated by 

 Professor Clark with reference to the structure and zoological position of 



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