624 Trow — The Karyology of Saprolegnia . 
so far as I have been able to observe, always follows the 
direct type : my observations on this point, however, might 
well have been more extensive. The chromosome loses its 
spherical character, becomes oblong, and soon after appears 
to have a slight median constriction. The two halves thus 
outlined gradually move apart until they are separated from 
each other by a distance equal to about the diameter of 
the originally spherical chromosome. The nucleus as a 
whole increases in size and alters in shape to accommodate 
itself to these internal changes. The nuclear wall, however, 
remains intact. Finally, a new nuclear wall appears in the 
plane of the equator of the nucleus, as is shown in Fig. 1 b , 
and the division is nearly complete. This wall later appears 
to split into two lamellae, for a constriction of the nucleus 
takes place in its plane and thus brings about a complete 
separation of the two daughter-nuclei. Further divisions 
follow, and while this is going on the germ-tube is developed. 
The apex of the germ-tube appears at all times to be destitute 
of a nucleus (Fig. 1 c and d). 
If we turn now to the study of the mature hyphae, sections 
of which abound everywhere in the preparations, we find that 
the nucleus is generally more or less elongated, and the chro- 
mosome alters its shape to keep pace with the change in the 
nucleus. The protoplasm forms a lining to the cell-wall, and 
encloses a large central vacuole, across which thin bridles or 
connecting strands of protoplasm sometimes stretch. The 
nuclei are fairly evenly distributed, but are sometimes to be 
found in groups in accumulations of the protoplasm. Divisions 
appear to take place regularly (except perhaps in those hyphae 
poor in protoplasm), and sometimes one sees very elongated 
nuclei like those in Fig. 2 b . as if a simultaneous division into 
more than two daughter-nuclei were to follow. 
Sporangia. Formation of Zoospores. The phenomena con- 
nected with the development of the sporangium and spores 
appear to be mainly of physiological interest. A hypha is 
arrested in its growth, and considerable quantities of proto- 
plasm pass into its apical portion. This apical portion filled 
