Bac'illar'ia.'\ iKFrsoniAL animalci^les. 225 



This remarkable appearance has its cause, perhaps, in the existence 

 of numerous delicate cilia, which are present over the surface of the 

 creature, and giving rise to the motion. 



"With om' present instruments we cannot take cognizance of 

 these organs ; but when making use of a very high power, a sort 

 of transparent narrow zone is observed around the bodies of the 

 Bacilhria. 



"Lastly, Ehrenberg adduces another observation as satisfactorily 

 proving the animal nature of the Bacillaria. They sometimes 

 receive colouring matter, which fills the vesicles looked upon by him 

 as stomachs. This last statement appears at least very striking, 

 but the way in which the case stands seems to be somewhat different. 

 In the first place, I can see no stomach sacs in the Navicidce, and 

 never observed in the living and moving Bacillaria the colouring 

 matter received at one extremity and carried towards the centre, 

 where these stomach sacs should lie, whilst in the Infusoria such 

 observations are easy ; on the other hand, it is not rarely found, 

 especially T\ith the larger living animalcules, that the molecules of 

 the coloui'ing matter employed, lie upon the middle of the broad 

 ventral surface, from wliich it appears as if the colouiing material 

 was really existing internally ; but if a glass plate is placed upon it, 

 and then properly removed, the globule of colom'ing matter may be 

 taken away. The imprejudiced reader must then see that much 

 obsen-ation is yet wanting ere we can hope satisfactorily to determine 

 that the Bacillaria are truly animals ; and how closely plants and 

 animals border upon each other is recognizable in the spermatic 

 animalcules of the lower plants, and the spermatic animalcules of 

 animals." (Jahresbericht, Berlin, 1839.) 



Since the date of Dr. Meyen's paper, much has been done to 

 augment our knowledge of the Bacillaria , and, in the opinion of 

 most natui'alists, also to indicate yet more their affinity with plants. 



The phenemenon of conjugation, so admirably investigated and 

 illustrated by IMr. Thwaites, is regarded as particularly indicative of 

 the vegetable nature of Bacillaria. In the Desmicliacea, the mode of 

 conjugation is the counterpart of that in the Zygnemeoi, (a tribe of 

 AlgceJ, producing a characteristic sporangium, but in the Diatomacea, 



