306 



Dr. H. H. Dixon. On the Structure of 



observations are made to Miss Delap and Mr. C. Green, who kindly 

 gathered the algse, the former at Valencia and the latter at Water- 

 ville, and posted them to me, to be then fixed in one or other of the 

 fixing fluids mentioned above. 



All the coccospheres found agree in their characters with Wallich's 

 Coccosjplicera ^elagica and all the free coccoliths observed are apparently 

 derived from that organism, all being oval and often possessing the 

 characteristic D-shaped apertures. Throughout my search I did not 

 find a specimen of Coccosphcera leptopoiv. of Murray and Blackman, so 

 that apparently this latter is absent from or very scarce in the ocean 

 near our coasts. 



The examination of fresh coccospheres in sea-water aff'orded no 

 evidence as to whether these organisms were alive or dead when col- 

 lected ; no protoplasmic protrusions could be seen extending from the 

 apertures in the coccoliths nor from the spaces between the coccoliths ; 

 nor could any spontaneous motion be observed in the coccospheres. 

 In sea-water the coccospheres appear quite colourless, except for the 

 bluish-green appearance of the covering coccoliths, due apparently 

 to the fact that their refractive index is higher than the water in which 

 they are immersed. No coloration due to the presence of an internal 

 chromatophore nor any sign of such a body could in any case be 

 made out. 



The absence of the chromatophore, recorded by Murray and Black- 

 man as occurring in C. leptopora, is not, I think, sufficient reason for 

 concluding that all the coccospheres examined had been for some time 

 dead, and so had lost their cell contents ; for the coccospheres were 

 in the great majority of cases quite perfect, and, as we will see later 

 on, the presence of proteid material and probably of a nucleus in a 

 large number of them was revealed by various stains and reagents. 

 Some, however, were devoid of contents or possessed so little , that 

 their presence eluded detection. 



External Characters, 



As Murray and Blackman* point out, there is considerable variation 

 in the size of Coccosphcera pelagica. Of about fifty specimens taken 

 at random and measured, the largest had a diameter measuring 0*0294 

 mm., and the smallest 0'0199 mm. This variation is in part due to 

 the inconstancy in the number of coccoliths on the coccospheres, and in 

 part to the varying amount of overlap of the coccoliths over one 

 another. The greatest number of coccoliths observed by me on one 

 coccosphere was sixteen and the smallest six. Eig. 1 (Plate 3) shows a 

 coccosphere captured in 1897 in Killiney Bay, having only six or seven 

 coccoliths upon it. Fig. 2 shows a fragment of another coccosphere 

 * *Phil. Trans.,' B, vol. 190 (1898), pp. 427—441. 



