188 Mr. H. J. Carter on Melobesia unicellularis, 



In the first place, there are two kinds of coccospheres, as 

 figured by Prof. Huxley (/. c. fig. 6, c, d) ; but I do not aUude 

 to his division of them into the " compact " and " loose " 

 ty]3es. One is formed exclusively of the frustules of Melobesia 

 unicellularis^ and the other as exclusively of the frustules of 

 M. discus — the latter, together with its frustules, much less 

 common than the former. Then, so far as my observation 

 goes, the frustules in the coccosphere of M. unicellularis vary 

 in size with that of this coccosphere, and never attain tlie dimen- 

 sions or fully matured appearance of the free individuals, but for 

 the most part retain that of those called by Prof . Huxley " disco- 

 liths." As the coccospheres vary a little in size, so the largest 

 free frustules are longer than the diameter of the smaller cocco- 

 spheres, and not far short of that of the larger ones, being in 

 the proportion of about 3^ to 4| GOOOths of an inch in diameter 

 respectively. After this, we observe that the frustules in both 

 kinds of coccospheres are compactly tessellated over the sur- 

 face of the coccosphere-cells respectively, recalling to mind 

 the way in which the gonimic contents of a unicellular Alga 

 (which, it should be remembered, are always confined to the 

 periphery and situated between the cell-wall and another more 

 delicate membrane internally, enclosing the aqueous cavity of 

 the cell) undergo division for a new progeny (see " Fecunda- 

 tion oi Eudorina^'' pi. 8. fig. 2, vol. ii. 'Annals,' Oct. 1858) — 

 and, lastly, that when the calcareous material of the frustules 

 on the coccosphere is dissolved away by acetic acid, a mem- 

 branous cell (that observed by Wallich) of the same size, with 

 a faint appearance of the frustules, still remains behind. 



Now, in the face of all this evidence, how can one come to 

 any other conclusion than that the coccospheres are the spo- 

 rangia of the two species of Melohesia respectively above de- 

 scribed ? And may not the division of the nucleus or central 

 granule, which we can trace in the frustules oi M. unicellularis 

 from a single to a multifid state, when it assumes a globular 

 form, be in some way connected with the reproductive pro- 

 cess, if not an early condition of the coccosphere or sporan- 

 gium? 



If it be satisfactorily jn'oved that Melohesia unicellularis is 

 an Alga, then both the first and second conclusions of Prof. 

 Huxley above quoted can be no longer retained ; and if the 

 frustules of M. unicelhdaris on their coccospheres can be 

 shown to be developed in proportion to the size of the latter, 

 then in the lower phases they represent Prof. Huxley's "disco- 

 liths." Hence my reasons for considering the latter immature 

 or young forms of M. unicellularis. 



The " loose type " of coccosphere figured by Prof. Huxley 



