316 C. CLIFFORD DOBELL. 
protozoan cell—no matter whether we see in it a primary 
nucleus and chromidial mass, or a vegetative karyosome in 
the nucleus, or even a separate vegetative and generative 
nucleus—in each case, but a single and simple nuclear 
apparatus before us.” The physiological nature of the 
karyosome is also well seen in the case of Actinospherium 
(cf. Hertwig, 98a). In well-fed animals the karyosome con- 
sists almost entirely of plastin, but in ill-fed individuals it 
comes to be largely composed of chromatin; and so on. Its 
different behaviour in different organisms is also to be noted. 
For example, in Himeira schubergi the macrogametocyte 
casts out the karyosome before fertilisation, whereas in H. 
lacazei it is retained. 
That the trypanosome blepharoplast is homologous with the 
centrosome I have elsewhere (’?08b) endeavoured to show. 
But I cannot in the least agree with the homologization of 
the blepharoplast with the karyosome. The centrosome, I 
believe, is an organ of nuclear origin, but originally not a 
nucleus. ‘The facts regarding the Protozoa and Metazoa! 
all appear to me to point in this direction. 
With Boveri (00) “I fully agree with R. Hertwig in that I 
do not hold a binucleate condition as the necessary starting 
point for the phylogenetic origin of the centrosome.” 
Phylogenetically, the centrosome probably arose, not from 
an originally present kinetonucleus, but as a differentation of 
part of an original single nucleus—in a manner indicated by 
Hertwig (95), Boveri, Calkins, etc. Hertwig himself believed 
the centrosome to be a specialisation of the central spindle, 
so that the spindle of Protozoa (e.g. Paramecium) is 
equivalent to centrosome + spindle of the Metazoa. In many 
groups of Protozoa it is possible to trace a fairly perfect series 
of nuclear types, from simple amitotic nuclei up to nuclei 
! Cases of centrosomes appearing in the cytoplasm independently of 
the nucleus are of course known. But here there is no proof that they 
did not originally come from the nucleus. (E.g. cf. Yatsu, “05, who 
admits that the centrosomes do not appear until the nuclear membrane 
has disappeared.) 
