106 JIEMOilANDA. 



In certain Infusoria there appears to be a more active vital 

 power than in others. Thus^ in Glaucoma, VorliceUa, &c., 

 the food-balls move very slowly, whilst in more highly 

 organized types the motion is more rapid. In the former 

 (especially such as are probably larval forms) , the contractile 

 vesicle appears to have the power only to form a row of 

 auxiliary vesicles around it; wliilst in Amphilephts (which 

 approaches the Planarians in its character), the Setifera or 

 bristle-bearers, and other types, it is more poAverful, and the 

 fluid is ejected with sufficient force to work its way into the 

 body, and form canals, or arteries, however primitive they 

 may be. The progressive vitality I have often noticed in the 

 same form at different stages of its growth. 



The foregoing remarks are not made for the purpose of 

 pushing forward my own views and opinions, for these must 

 necessarily become changed or modified as the science pro- 

 gresses; but with a view to direct observation to the subject, 

 and obtain for it a greater share of the attention of English 

 microscopists than has hitherto been bestowed upon it. — 

 James Samuelson. 



When are Diatoms common in a Slide ? — All who have 

 received gatherings of diatoms have been frequently puzzled 

 by the observations which accompanied them in regard to 

 the scarcity or abundance of a particular species; and it 

 appears to me that some law on the subject would be of 

 essential service, and might save many from disappointment. 

 Unless it be mentioned that the species sought is only to be 

 met with in the heavier or lighter portions, it is understood that 

 the average is intended, as obtained by shaking the little 

 tube in which the preparation or " boiling " is kept ; and 

 with that miderstanding, the following observations will 

 indicate the principles on which more definite terms may 

 be founded. 



Dr. Gregory, in last number of the ' Micr. Soc. Trans.,' 

 enumerates 304 species found in the Glenshira Sand, of 

 which, however, a few appear not to be diatoms ; some sup- 

 posed new, seem (if one may judge from the descriptions 

 and figures) to be only varieties of well-knoAvn species, and 

 others are of that extreme scarcity as not to form tu^o P^'^ 

 cent, of the preparation, and therefore are to be seen in few 

 of the slides ; on no one slide can there be said to be 200 

 species. Again, according to Smith's Synopsis of Diato- 

 maceae, there appear to about 500 species in Great Britain ; 

 as nearly one half of these are marine, the rest from fresh 



