Dr. Henri Blanc on Ceratium Iiirundinella. 449 



a Ceratium first of all observed in the living state, and wliich 

 I succeeded in preserving in Canada balsam, after having 

 fixed it by means of picro-sulphuric acid and stained it with 

 picro-carmine. The nucleus of this Ceratium is not of the 

 usual form ; it is less elongated, for instead of measuring 

 0*030 millim. in length bj 0"010 millim. in breadth, it is not 

 more than 0'023 millim. long by 0'013 millim. broad — that 

 is to say, it has now the form of a regular oval. Moreover, 

 instead of having a single nucleolus, this nucleus contains 

 two of them, placed excentrically, at a distance from each 

 other. Whence do these two nucleoli originate ? Is one of 

 them the nucleolus generally observed in every nucleus, 

 while the other has been formed independently at the expense 

 of the chromatic substance ? or are they both the products of 

 the division of a single nucleolus? Although I have no 

 observations to prove it, I can nevertheless assume that these 

 two nucleoli are the products of the division of the single 

 nucleolus which occurs in every elongated nucleus. In fact 

 if one of them had been formed at the expense of the chro- 

 matic substance, the latter would have undergone some 

 modification in its mode of distribution ; or among the nuclei 

 examined, which possessed two nucleoli, I must necessarily 

 have met with at least one possessing one nucleolus smaller 

 than the other — that is to say, in a condition of growth. I 

 have never been able to observe either the one or the other 

 of these two facts ; the distribution of the chromatic substance 

 in the intei'ior of the nucleus was always the same, and the 

 two nucleoli always possessed the same diameter. 



Fig. 7 represents a Ceratium of which the nucleus has 

 undergone a notable transformation as regards its form. It 

 is neither elongated nor oval, but is strongly constricted in 

 the middle, and appears to be incompletely divided into two 

 exactly similar halves, each possessing a nucleolus. The 

 contents of the nucleus in this specimen are still the same as 

 in that above described ; we remark no peculiar arrangement 

 of the chromatic substance. 



Fig. 8 represents an interesting individual, observed and 

 drawn in the living state, but which, to my great regret, 

 could not be preserved in Canada balsam. What strikes one 

 first of all in this specimen is that its nucleus does not occupy 

 the usual position ; instead of being situated almost entirely 

 in the posterior [anterior] region of the body, below the circlet, 

 it is placed across the latter. As in the preceding individual, 

 the nucleus still appears as if divided into two equal parts j 

 but the central part which unites them is much more slender.- 

 Important modifications are also to be observed in the 

 Ann. & Ma(j. N. Uiat. Ser. 5. Vol. xvi. 31 



