KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 5 



thousand feet offshore. Collections were taken at intervals of four hours 

 throughout the day and night. In addition to these collections another series 

 was made intermittently during the summer of 1917 at distances of two to five 

 miles offshore over depths of one hundred to six hundred fathoms. 



The success we have attained in securing the striking representation of the 

 group here revealed has been due to the opportunity to get living material 

 promptly into the laboratory from oceanic conditions some distance offshore. 

 This was accomplished in tlie sunnner of 1917 by certain modifications of the 

 earlier methods, which had involved the use of short tow nets of No. 20 silk 

 bolting cloth with an opening of fourteen inches in diameter and a length of 

 about fort}' inches. The amount of plankton taken in these was large, and 

 presumably only the hardier species survived the crowded conditions and the 

 delay attendant upon bringing in the collection by the slow motor boats then in 

 use. In 1917 a smaller net, five inclies in diameter and fifty inches in length, of 

 No. 25 silk bolting cloth (the equivalent of No. 20 of earlier years in having 

 approximately 40,000 meshes per square inch) was adopted. This was lowered 

 to a depth of eighty meters, three to six miles offshore, towed at that level 

 slowly for twenty minutes and then brought to the surface by hand. The 

 bottom of the net terminated in a four-ounce, wide-mouthed bottle, which was 

 tied in the end by a lashing and served as a detachable plankton bucket. The 

 catch was transferred at once to a quart jar of fresh sea water and hurried 

 to the laboratory liy speedy motor boat for examination, with the result that 

 these delicate animals were f omid in unprecedented frequency and exceptionally 

 fine condition. 



The amount of plankton during the summer months of 1917 was at no time 

 large, and often the catch in the bottle was so small as to be scarcely visible 

 to the naked eye. For this cause, as well as by reason of the small orifice of 

 tlie net, the catch was small, and owing to the relatively large filtration surface, 

 c()m])uted to be four times the area of the orifice, the rate of movement of the 

 water through the minute orifices of the silk was not rapid enough to destroy 

 the delicate Gymnodinioidae of the plankton. Furthermore, owing to the 

 absence of crowded conditions in our small catches and to the fact that the 

 "Ellen Browning," the fast boat of the Biological Station, has a speed of 

 thirty miles an hour, it was possible to convey the catch to the laboratory in a 

 quite normal condition. 



A list of the earlier collections, most of which have been examined in fresh 

 and preserved condition, will be found in Ritter d al. (1915, p. 156) in the list 

 of Preliminarij planldon collections. Preserved collections of plankton are of 

 no value in the study of this group except for records of the occurrence of a 

 few of the more highly resistant and specialized forms, such as Polijkrikos and 

 Gi/mnodiniiim lira, and even these ai-e rarely found in such collections. Most 

 species do not survive the ordinary application of reagents used in preservation, 

 such as formalin. 



