Sturck. — Harvey el la mirabilis ( Schmitz & Reinke ). 89 
1. The much-branched filaments growing in the interior 
of the host, which absorb nourishment from the contents of 
the host-cells. Glycerin-material stained with Hoffmann’s 
blue, enables one to see distinct protoplasmic threads 
connecting the cell-contents of these filaments with the 
cell-contents of the Rhodomela. The distal cells grow and 
divide in a similar way to the distal cells of the peripheral 
chains, producing sub-dichotomously branched filaments, but 
these filaments are as a rule much more copiously branched 
than the peripheral chains. 
2. A hemispherical external portion, consisting of — 
(a) The small-celled peripheral layer, four or five cells 
deep, the cells being arranged in monosiphonous more or less 
branched filaments. This peripheral layer gradually passes 
over into 
(b) The large central mass of larger cells. In the ordinary 
adult thallus these cells are oblong, slightly rounded, and 
obviously arranged in radiating branched filaments ; but at 
the time of the development of trichogynes or tetraspores 
these cells become gorged with contents and are often almost 
circular in outline, and so crowded together that their 
filamentous arrangement is not so easily seen. 
The whole external part of the plant is enclosed in a fairly 
thick gelatinous membrane, which is sometimes structureless, 
but can be occasionally seen to be made up, especially in 
its inner portion, of the fused gelatinous walls of the peri- 
pheral cells. The walls of all the cells are fairly thick. The 
contents of all the cells of Harveyella mirabilis are quite 
colourless, except when some of the outermost peripheral cells, 
as previously mentioned, become stained brown. Glycerin- 
material stained with Hoffmanns blue shows that the peri- 
pheral cells, and the cells of the filaments inside the host, 
stain much more deeply and rapidly than the cells of the 
central mass of tissue. The nuclei of the cells stain well with 
Hoffmann’s blue. 
During the growth of the parasite, a number of the cortical 
and some of the larger cells of the Rhodomela often become 
