RECENT RESEARCHES IN THE DIATOMaCE.E. 243 



Within a few months after the important discovery of 

 Dr. McDonald had been made known, and before the paper 

 had come under the notice of Dr. Pfitzer, the latter had 

 worked out the same conclusion, thus corroborating the 

 views of Dr. M'Donald, without derogating in the slightest 

 degree from the credit due to himself for his own independent 

 observation. 



It must be remarked that the theory just stated as to the 

 nature of the hoop and its bearings on the development of 

 the frustule, has been established only in regard to the genus 

 Biddulphia and its kindred families. The supposition that 

 the same character belongs to the hoop in the other nume- 

 rous genera is but a presumption — a very natural one, indeed, 

 but still it needs confirmation. 



This fact opens up a wide field for research, and it is 

 hoped that the numerous students of the Diatomacecs 

 throughout the world will be prompted to follow out the 

 track the discoveries of Wallich, M' Donald, and Pfitzer have 

 indicated. 



II. 



The subject of the former notice of Dr. Pfitzer's useful and 

 instructive treatise was the structure of the external siliceous 

 epiderm of the Diatomacea. The information afforded by the 

 author on this subject cannot fail to interest the most ex- 

 perienced student of these forms, and much of it will be quite- 

 new to those who have been satisfied with a superficial 

 inspection of the most obvious characters of the diatomaceous 

 frustules. 



My present purpose is to convey to my readers the views 

 of the author regarding the contents of the cell ; a depart- 

 ment of the subject which has not received the attention it 

 deserves. There are many students who confine their atten- 

 tion to frustules which have been treated with acid ; to such 

 the characters of the cell-contents must be altogether 

 imknown. There are others, it is to be feared relatively few 

 in number, who, not content with such superficial knowledge, 

 desire to understand the most recondite details of structure. 

 Such researches are attended with considerable difficulty, in 

 consequence of the normal condition of the cell-contents 

 being affected by circumstances, and the application of re- 

 agents being often necessary to bring out the details with 

 sufficient distinctness. The information given by Dr. Pfitzer 

 on the structure of the cell-contents of the diatomaceous 

 frustule is therefore the more important and deserving of 

 attention. 



VOL. XII. NEW SER. S 



