ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 469 



to fheir nature. He considers that they must be either parasitic 

 Peridinise or endogenoiis buddings. There are generally found dia- 

 tomin-bodies of definite form ; but their form and arrangement differ 

 widely in the different species. Pure green Peridinise were never 

 seen. Besides these coloured, there are also colourless species or 

 varieties, such as Peridinium diver gens and Diplopsalis lenticula ; 

 Gourret describes colourless forms of Ceratium. Starch-grains (even in 

 one colourless species) and yellow and red drops of oil, occur in vary- 

 ing quantities ; definite eye-spots could not be detected. The so- 

 called contractile vesicles described by Stein are nothing but ordinary 

 vacuoles. 



As in the fresh-water forms, the propagation of the marine also 

 takes place by longitudinal division. Usually this occurs when at 

 rest ; after the division is completed, the cell-wall bursts, and the 

 products of division escape invested in jelly. This division is more 

 or less oblique, and one of the segments lies therefore higher than the 

 other. The division is sometimes incomplete ; and from this result 

 the so-called " copulation conditions " of Stein. The apposition of 

 tvvo individuals, as observed by Pouchet, is no copulation, but a 

 biological phenomenon, an adaptation to pelagic life, which leads, in 

 several forms, to the formation of chains. Another peculiarity of the 

 Peridiuige is the frequent excoriation, the course of which, the author 

 describes ; and which takes place especially on any change in the 

 vital conditions, as the result of rapid encysting. 



With reference to the classification of the Peridinise, the author 

 objects to splitting them up into a number of new genera, as Stein 

 proposes, depending on the comparative structure of the cell-wall ; 

 and considers it preferable to retain the old limits of the genus 

 Peridinium, He also differs altogether from the suggestion of Stein and 

 Pouchet, of an alliance with the NoctilucaB, and maintains his previous 

 view, according to which the Peridini^e behave as algse in their 

 structure and history of development, and must be placed in the 

 Thallophytes. Forms like Exuviaella marina and Prorocentrum 

 present a passage to those algae which occur as yellow cells in so 

 many Eadiolaria and other animals. It cannot, however, be denied 

 that the Peridinise exhibit also some relationships to the remarkable 

 middle group of the Plagellata ; organisms like Exuviaella and Proro- 

 centrum presenting resemblances in the form of the body, the attach- 

 ment of the cilia, and the diatomin, to the Cryptomonads ; although 

 Bergh has shown, in the case of Prorocentrum, that the relationship is 

 not sufficient to indicate a direct descent of the Peridinise from these 

 Flagellata. 



Marine Peridinise.* — M. G. Pouchet describes a number of marine 

 Peridinias, among which Protoperidinium viride, Glenodinium obliquum, 

 Gymnodinium pulvisculus, crassum, teredo, pseudonoctiluca, and arcJii- 

 medis are new. He discusses the systematic position of the group, 

 and points out that they approach plants in having an envelope of 

 cellulose, diatomine, or even chlorophyll, and two flagella, like the 



* Journ. Anat. et Phybiol. (Robiu), xxi. (1885) pp. 28-8S (3 pis.). 



