MEMORANDA. 307 



50 of the larger instruments for which the medals should be 

 awarded. 



" The members will be glad to learn that for these prizes 

 there have been numerous competitors. After most carefnl 

 examination of all the instruments by the Committee, they 

 unanimously reported to the Council that the instruments 

 sent in by Messrs. Field and Co., of Birmingham, fulfilled 

 all the conditions required, and the Council have, therefore, 

 awarded to that firm the medals offered, on Messrs. Field and 

 Co. entering into the necessary undertakings to comply with 

 the requirements of the Prize List. The Council congratulate 

 the members on this result. Those members who are desirous 

 of securing any of these instruments, which will shortly be 

 supplied to the Society by Messrs. Field, at a discount of 

 10 per cent., should at once send in their names to the 

 Secretary." — Excerpt Annual Report of the Council of the 

 Society of Arts to the Members, presented at the General Meet- 

 ing, June 13, 1855. 



On " Species " of Diatoiuaceie. — In your Journal for January 

 Professor Smith has made some valuable observations on what 

 is a species among Diatomaceae, in which he enforces the 

 necessity of studying these beings in the recent state before 

 one can decide on what ought to be reckoned distinct. This 

 is the more necessary as it appears to me that neither size of 

 the frustules or distance of the striae are sufficient to distin- 

 guish species, unless we allow to each a very considerable 

 range of variation. 



What are called "species" in Diatomace2e may be viewed 

 under a twofold aspect : — 1st. A species as it exists in nature, 

 requiring a study of every state from the sporangium to the 

 sporangium-bearing individual : 2nd. As serves the purposes 

 of the microscopist, who gives names to every difference of 

 form or size he observes that is not already figured. To the 

 latter class may be referred most of Ehrenberg's, Kiitzing's, 

 and Gregory's species ; and it would be preferable to indicate 

 them by 1, 2, 3, &c., to giving names to each, until Smith or 

 some other naturalist can ascertain to what genuine species 

 such forms mav be referred. It is a natural species alone 

 which is worthy of the attention of scientific men. 



A diatom increases in two different ways — by sporangia, 

 and by self-division. The length of time before a diatom 

 produces sporangia probably varies considerably in different 

 genera, and even in different species, but seems rarely, if ever, 

 to be less than three or four months. On the other hand the 

 power of self-division, although supposed by some to belong 



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