100 MEMOIES OF THE UNIVERSITY OF CALIFORNIA 



lu our discussion of occurrences we have noted the depth from which the 

 net was drawn in making the collection. The net was towed for ahoi;t twenty 

 minutes at the depth indicated, and then brought open to the surface. The 

 organisms in the catch maj' have come from any level. 



HISTORICAL DISCUSSION 



It is to the epoch-making work of O. F. JMiiller that we owe our first glimpse 

 of the members of the dinoflagellate group. The first of these to ])e discovered 

 were the fresh-water theeate forms of Ceratium hinindincUa and a species of 

 Peridinium. The former he called Bnrsaria MriindineUa and the latter Vorti- 

 cella cincta (1773) . In a later work (1777) he records the discovery of a marine 

 species also belonging to the genus Ccratinm, as Cercaria tripos. The outlines 

 of these forms were delineated with a fair degree of accuracy, but it was only 

 iu the species of Peridiuinm that the girdle was clearly marked. 



Miiller was followed by Schrank (1793), who established the genus Ceratium. 

 for a marine form which he designated C. tetraceras. 



The most important of these earlier observations, however, were those of 

 Michaelis (1830), who discovered that the phosphorescence of the sea was due, 

 in a large measure, to these minute forms of animal life. He figured a nuuiber 

 of species, among others Prorocentniin niicans, which were later named by 

 other investigators. He also was the first to observe the longitudinal flagellum, 

 though mistaking the single one, with its constant activity in a cone-shaped 

 amiilitude of vibration, for se^'eral flagella. 



In the same year appeared the first of a series of papers by Ehrenberg in 

 which some attention was given to this group. Like his predecessors, the 

 organisms which he observed were mainly those of the theeate forms. He de- 

 scribed the genera Prorocoitnnn, Glcnodininm, and Peridinium, describing 

 under the latter designation species which were later removed to the genus 

 Ceratium. In addition to these he described Gymnodinium. fuscuni as a species 

 of Peridinium. He observed the flagella characteristic of the group, though 

 figuring the ribbon-like transverse flagellum as a series of cilia. He also figui'ed 

 the girdle and sulcus. 



The first attempt to form a systematic group of the dinoflagellates was also 

 made by Ehrenberg (1830) in establishing the family Peridinaea for the genera 

 Peridinium and Glenodinium, to which he later added the genus Pino phy sis. 

 This grouping was based on a recognition of the relations of flagella and girdles. 



The genus Proroccntrtim was not recognized by Ehrenberg as related to 

 Peridinium, but was placed with the cryptomonads. His interpretation of the 

 internal structures of these micro-organisms was in line with his conception 

 of the Protozoa generally as more or less perfect miniature replicas of the 

 Metazoa. Thus the vacuole he considered as a stomach, the chromatophores as 

 ovaries, and the nucleus as a prostate gland. 



