60 GENERAL HISTOBY OF 



wliicli he has named Polycystinea. Several genera of an anomalous 

 form, which he at first classed "ndth Bacillaria, he has since united 

 M'ith others subsequently discovered under the above-named appella- 

 tion. As, however, the internal organization of the Pohjcystine^ is 

 unknown, Elu-cnbcrg contents himself by pointing out their agree- 

 ment with Pohjgastrica in their siliceous coating (ha-ving chiefly in 

 view the doubtful Bacillaria) and microscopic magnitude, whilst he 

 indicates, as a distinctive character, the existence of transverse arti- 

 culations in the Polycystinem. 



It would be but an exercise of the imagination to seek after 

 resemblances between the majority of the Infusoria and higher 

 animals, the resemblance could be but fenciful, existing only in 

 external form. In studj-ing the Infusoria, the mind should be un- 

 biassed by a knowledge of the organization of higher animals ; we 

 ought not to set out with the assumption that such living atoms must 

 be furnished with the organs of superior existences, and then indulge 

 the imagination, by accommodating appearances, observed to our pre- 

 conceived notions ; but we should rather endeavour to learn under 

 what simple conditions and contrivances, animal life can be manifested 

 and continued. 



The so-called class of Polygastrica must still be looked upon as an 

 heterogeneous collection of organic beings, which requires the careful 

 and persevering industry of observers to exclude aU forms not truly 

 animal, as well as those not having a specific identity, i. e., which 

 are but transitional embryonic forms. Numerous have been the bodies 

 removed from the lists of Infusoria of the older microscopists, by the 

 advance of microscopic knowledge, and by the improvement of the 

 microscope ; and we may yet look for equally great modifications of 

 the existing systems, from the genius and ai'dour of modern research, 

 especially on the subject of embryology. 



Since few doubt the expediency of separatiag the Closterina, and 

 many advocate that of removing the Bacillaria fi'om the animal 

 Infusoria, we shall defer considering the affinities of those families 

 (which lean rather to the vegetable than to the animal kingdom) to 

 the section especially devoted to them. 



As some remarks occm-red, in the fii-st edition of this work, relative 

 to the nature of spermatozoa, it may be right to state that the 



