Hazen: Lire HISTORY OF SPHAERELLA LACUSTRIS 2385 
successful has been the use of Sachs’ food solution. Good light 
and aération also encourage longer movement. It has been 
thought (Cohn '50) that zooids kept in the dark would not pro- 
duce secondary generations, and very generally I have found this 
to be the case ; such a condition might easily be accounted for by 
the fact that the darkness does not allow a growth vigorous 
enough to promote this asexual division. Zcoids kept in dark- 
ened cultures generally remain small, and after some days it will 
be found that they are narrower and more attenuated anteriorly 
than those kept under normal conditions (Fig. 36). That second- 
ary, division is not impossible, however, in cultures to which light 
has not been admitted, is proved by the fact that I have sometimes 
found cells producing zooids of the second or third generation 
after two days in such cultures (Fig. 31). After the zooids have 
finally come to rest and acquired a thick, permanent cell-wall no 
further division will take place until after some change in the 
environment. Alexander Braun ('51) stated that desiccation must 
intervene ; otherwise the cells would become blanched and lifeless. 
. Often my cultures have confirmed this opinion, but during the 
present winter I have repeatedly found that freezing will meet the 
requirement justas well ; in fact, propagation has been more vigor- 
ous after freezing than after drying, possibly because desiccation is 
sometimes too rapid in a warm room. 
Dangeard ('88) says that he kept resting cells in the bottom 
of a vase for a year without desiccation and then, when they were 
transferred to damp cells, division occurred. Nevertheless it is not 
impossible that freezing or a new food me brought about the 
required change in this case. 
RELATION OF SPHAERELLA NIVALIS TO S. LACUSTRIS 
Rabenhorst ('68) expressed a doubt as to the distinctness of 
these two species. Rostafinski (’75) after studying for four years 
the development of the species then called Chlamydococcus pluvi- 
alis, but without having seen C. mivadis, united the latter with the 
former under the name Haematococcus lacustris (Girod) Rostaf. 
The grounds for making this union were (1) The similarity of the 
development of the two species as shown by the comparison of 
some (apparently unpublished) drawings of C. nivalis by Schimper 
