McAllister . — Nuclear Division in Tetraspora lubrica. 685 
It is of interest here to note that according to the account of Lauterborn 
(29) the nuclear division in the diatom Surirella , — unlike that of any other 
known plant, — has much in common with the type of mitosis that is reported 
for Acantkocystis, Par amoeba and other forms. According to Lauterborn’s 
account, a central spindle is formed from a ‘centrosome’ lying outside the 
nucleus. The chromatin forms a spireme which breaks up into long 
chromosomes. The chromosomes become arranged about the cylindrical 
central spindle in the form of a ring. The ring-like mass separates into two 
groups which move to the poles where they organize the daughter nuclei. 
The general details as to the formation of the central spindle may 
be said to be confirmed by Karsten (25) in his recent work on the reduction 
division in Surirella saxonica. Karsten shows clearly that here the spireme 
thread is organized from the reticulum independently of the nucleole. The 
relationship of this peculiar group to the Chlorophyceae is undoubtedly 
very remote. 
Though differing somewhat as to the exact location of Tetraspora in 
the classification of the Chlorophyceae, nearly all students of the Algae 
seem agreed that the relationship of this group to the Chlamydomonadaceae 
is very close. There seems to be similar agreement in regarding the latter 
group as being the lowest of the green plants. Gay (18), Wille (53), 
Oltmanns (39), Chodat (7), and West (51) are practically in accord in 
placing the Volvocaceae as the lowest family in the order Protococcales 
with the Tetrasporaceae (or Palmellaceae) as the family next in order. 
Collins ( 8 ) places the Tetrasporaceae between the motile unicellular forms 
and the motile colonial forms. 
Since Reinke’s account (41) of the life history of Tetraspora in 1878 
practically no work has been done upon this interesting genus. Brief 
references by Gay (18), Chodat ( 6 ) and West (51) seem to confirm, however, 
the details of this life history. Biciliate zoospores are reported and 
smaller biciliate isogametes. The latter fuse to form a zygote which, — 
according to Reinke, retains the cilia of the two gametes and swims about 
for a time evidently entering into a resting stage at a later period. Only 
very meagre references are made to the details of the structure of the cell. 
The Tetraspora species which has been used in this study is common 
in the vicinity of Ithaca, N.Y., growing in shallow running water attached 
to the rocky bed of the stream. The lamellate, gelatinous colonies are 
usually buoyed up by entangled bubbles of gas. The length of the gela- 
tinous masses varies from ten to forty millimetres, the diameter being from 
four to ten millimetres. The cells of the colony are approximately spherical 
and vary in diameter from seven to thirteen microns, depending of course 
upon the amount of growth which has taken place since the last division. 
The material agrees with the description of Tetraspora lubrica in many 
respects, though the characterization is not entirely satisfactory. All three 
