934 
THE VOYAGE OF H.M.S. CHALLENGER 
Diatoms were taken in the tow-nets, this was regarded as indicating the presence of coast 
water. A few species of Infusoria belonging to the above-mentioned genera are, however, 
constantly met with far from land attached to Diatoms, Radiolaria, Copepods, dead shells 
of Spirilla, and other organisms. 
Ceratium ( Peridinium ) tripos was very frequently observed in chains, from two to 
twenty-one being attached together, as shown in the annexed woodcut (fig. 334). Although 
Ceratium tripos occurs in great abundance in shore waters, occasionally filling the tow- 
nets with a yellow coloured slime, it was only observed in catena in the open ocean far 
from land. Neither flagellum nor cilia were observed in the chains of Ceratium tripos ; 
a similar observation is recorded by Ponchet. 1 There appear to be good reasons for 
regarding these organisms as unicellular Algae rather than Infusoria. 2 
1 Sur revolution des Peridiinens, &c., Comptes rendus, t. xcv. p. 794, 1882 ; Contribution a l’histoire des Cilio- 
flagelles, Journ. de I’anat. et'phys., t. xix., No. 4, 1883. 
2 Mr. J. T. Cunningham, who has recently been making observations on these organisms at the Scottish Marine 
Station, writes : — “The possession of greatly developed horns, or arms, of a flattened triangular body, and of a large 
aperture in the case interrupting the equatorial groove, distinguishes the genus Ceratium from other Peridiniida?. The 
genus was instituted by F. von Paula Schrank. Ceratium tripos, the most conspicuous species, was first described by 
0. F. Muller under the name Cercaria tripos. C. L. Nitsch first gave it its present name. 
“ Dr. I>. S. Bergh* has recently published investigations on the nature and affinities of the Cilio-flagellata, and gives 
a complete discussion of the species of Ceratium. He treats the question from a morphological point of view, and believes 
* Dei- Organis'jius fler Cilioflagellaten eine phylogenetisclie Stiulie, Morph ol-. Jahrb., Brl. vii. pp. 177-288, 1882. 
