PLANKTONIC STUDIES. 585 
inelude here a great number of protista, which have hitherto been 
reckoned as protozoa, e. g., the Murracytea, Dictyochee, Peridinee. 
As characteristic and important protophytes of the plankton I here 
mention sevea groups: (1) Chromacea, (2) Calcocytew, (3) Murracytee, 
(4) Diatomea, (5) Xanthellee, (6) Dictyochew, (7) Peridinee. 
1. Chromacec (30, p.452).—In this lowest vegetable group is probably 
to be placed a number of small “unicellular algie” of simplest form, 
which occur in great abundance in the plankton, but on account of 
their minute size and simple spherical shape have for the most part 
been overlooked, or possibly regarded as germ cells of other organisms. 
They may here be provisionally distinguished as Procytella primordialis. 
The diameter of the spherical cells in the smaller forms is only about 
.001 to .005 mm., in the larger .008 to .012 mm, seldom more. Usually 
each cell contains only one phytochrom granule of greenish color, 
sometimes approaching a yellow or red, sometimes a blue or brown. 
Whether there is also a diminutive nucleus is doubtful. Increase takes 
place simply by division into two or four parts, and appears to go on 
with excessive rapidity, but swarm spores do not appear to be formed. 
Hundreds or thousands of such green spheres may be united in a mass 
of jelly. The decision whether these simplest Chromacew belong to the 
Chlorcoccee or Protococcea, or to some other primitive protophytic group, 
must be left to the botanist for further investigation, as well as the 
question whether these diminutive Procytelle are actually true nucleated 
cells or only unnucleated cytodes. For our plankton studies these are 
of interest only so far as they develop in astonishing quantities in many 
(the colder) regions of the ocean, like the diatoms; and with the latter 
form a great part of the fundamental food (Urnahrung). Over wide 
areas the sea is often colored brown or green, and they form the chief 
food (described as Protococeus marinus) of inconceivable myriads of : 
copepods, as Kiikenthal has mentioned in his “Contributions on the 
Fauna of Spitzbergen.” j 
2. Calcocytee.—In the eighth edition of the “ Naturliche Schopfungs- 
geschichte” (30, p. 437) I have designated as Caleocytew or “unicellular 
calcareous alge” those important minute organisms which, as “ Coc- 
cosphera, Cyathosphera, and Rhabdosphera, play a great role in oceanic 
life. They are found abundantly in the plankton of the tropical and 
subtropical seas, less abundantly in colder zones, and are never absent 
where pelagic Thalamophora occur in great numbers. Like the latter, 
theyarebathypelagic. Theball of protoplasm which completely fills the 
interior of the small ealeareous-shelled plastid seems, when stained red 
with carmine or brown with iodine, to be unnucleated, and therefore a 
cytode. The beautiful calcareous plates which compose the shell ( Cocco- 
litha, Cyatholitha, Rhabdolitha), and which in the Rhabdosphera bear a 
radial spine, fall apart after death and are found in great numbers in all 
parts of the warmer oceans and in the globigerina ooze of the bottom. 
Murray (5, p. 533; 6, p. 939) and Wyville Thompson (14, 1, p. 222) 
