8 
Davis. — Spore Formation in Derbesia. 
as two rings, one below the other, the lower slightly larger than the upper, 
so that it appears somewhat outside when the blepharoplast is viewed from 
above (Figs. 22, 24). 
The cilia, as stated before, arise as outgrowths from the lower ring 
(Figs. 22, 25, 26). It was not possible to determine whether each cilium 
was connected with a definite granule such as entered into the composition 
of the blepharoplast, for the latter has the appearance of being an homo- 
geneous structure. It stains evenly, and the granules that formed it 
(Fig. 18) fuse together so completely that their individuality becomes lost. 
The splitting of the primary ring is a very curious process, for which I 
have no explanation to offer. 
Mention has been made of the occasional binucleate spore origins. A 
section of such a one is shown in Fig. 27, so far advanced in its develop- 
ment that its blepharoplast is formed. There can hardly be doubt but 
that such an example would give rise to a binucleate zoospore. The 
development of such a zoospore simply means that the progressive segmen- 
tation of the protoplasm by the branching cleavage furrows does not always 
proceed far enough to separate all of the large nuclei from one another. 
During the development of the zoospores some important changes 
take place in the structure of the nucleus. As shown in Fig. 6 , the 
nuclei which enter the sporangium contain two structures : (1) the deeply- 
staining relatively small nucleolus, and (2) a large homogeneous body 
which is chromatic in character, as proved by its later history, and which 
I have called the chromatin body. This latter structure remains un- 
changed in appearance during the differentiation of the nuclei in size 
(Fig. 7), but later, changes become apparent within the large nuclei. 
Delicate strands appear in the nuclear space, forming a loose network 
(Figs. 8, 10), and the chromatin body ceases to be homogeneous in structure 
but becomes instead granular or cloudy. Finally, the nuclei at the time 
of the segmentation of the protoplasm to form the zoospores (Figs. 12, 13) 
contain loose masses of cloudy material connected by strands to form an 
irregular network. While the blepharoplast is being developed the net- 
work becomes more and more conspicuous and stains more deeply 
(Figs. 1 6, 19). The cloudy masses at last practically disappear, and there 
are present in the nucleus coiled threads, generally somewhat gathered 
in the centre near the nucleolus (Figs. 21, 24). These coiled threads are 
clearly chromatic, and from them is organized the spirem of the first 
mitosis in the germinating spore. 
Perhaps the most important result of the present study of Derbesia 
is the clear evidence that the nucleus is concerned in a most intimate 
manner with the development of the blepharoplast. The nucleus leaves 
its position in the centre of the cell, the radiating protoplasmic strands 
over a certain portion of its surface take a definite position in the form of 
