1 29 



NOTES AND COMMENTS. 



IMPORTANT WORK OX DIATOMS.* 



The completion of this great work, which has been appearing 

 in parts throughout the past eleven years, will be hailed with 

 pleasure by all students of the Diatomacese. Though ex- 

 . pressly intended to deal with those forms that are found on all 

 the coasts of France, it will be found to contain most, if not all 

 of the species of the North Sea and English Channel, and is 

 hence equally valuable to English students. The plates are 

 certainly among the finest drawings of these beautiful micro- 

 scopic Algae that have ever been published. Specially worthy 

 of notice are the discoid forms of Actinocyclus, Coscinodisciis 

 and Eiipodiscus, and the wealth of detail in such species as the 

 Naviculas of the Diploneis section. 



EVOLUTIOX OF DIATOMS. 



M. Peragallo's views on the evolution of the Diatoms are 

 set forth in a sort of postscript to the preface accompanying 

 the issue of the final part, and are in some respects both novel 

 and interesting. He holds that the earliest forms of diatoms 

 were of the kind he denominates ' Centriques ' (corresponding to 

 Van Heurck's ' Crypto-Raphideae ' ) , and comprising all forms 

 of circular or angular outline, and those having spines or other 

 processes, and that these descend directh' from animal forms, 

 either from the Radiolariae, or in part from the Peridineae. 



PLAXKTOX. 



The ' Centriques ' are those species that we find to-day float- 

 ing on the ocean in what is known as the ' Plankton ' and are 

 distinguished from the ' Pennees ' (Peragallo's other division) not 

 only by their form arranged at about equal distances around a 

 centre, and by the absence of a raphe, but also by their repro- 

 ductive method, which is by the generation of spores, whereas 

 the ' Pennees ' reproduce their kind by conjugation. The author 

 describes how the free-floating, but individually motionless 

 * Centriques ' developed in the ' Pennees ' to a naviculoid or 

 boat-shaped form with a raphe or longitudinal slit which is now 

 generally acknowledged to be in some way the organ of the 

 mysterious power of motion of diatoms. This division con- 

 stitutes Van Heurck's'' Raphideae.' 



* 'Diatomees Marines de France,' by M.M. H. et 'M. Peragallo. 

 J. Tempere, Grez-zur-Loing (S-et-M) France. 560 pp., 139 plates, 

 2187 fig., 150 francs. 



iqo9 April i. 



