No. 382.] REVIEWS OF RECENT LITERATURE. 793 
likeness in color to its background the bryozoan escapes detection 
when extended from its capsule. From the structure of the sponge 
it is evident that it is not located upon the bryozoan until the latter 
has attained a considerable growth. 
Although a considerable number of new species are described in 
this report, we find an occasional reduction of an old species to a 
Synonym as a result of the examination of this fauna through several 
seasons, and a few incidental references to the variability of characters 
relied upon for specific distinctions. Cranes A. Kordin. 
UNIVERSITY oF ILLINOIS, URBANA, ILL. 
Lake Fauna. — The results of three summers’ careful investiga- 
tion of the life in a small lake in Finland are given in a faunistic- 
biological paper by Dr. K. E. Stenroos,! which amply proves the 
sufficiency of a small body of water to yield a rich fauna and to throw 
light on many important biological problems. Lake Nurmijarvi con- 
tains but two square kilometers, is but one meter in depth, presents a 
variety of shore formations, and is rich in vegetation. It is subject 
to considerable fluctuation in level and in temperature and to much 
shifting of the bottom by the ice in winter. 
The author’s faunal list includes 460 species, of which 157 
belong to the Rotifera and 98 to the Entomostraca. The absence of 
nematodes, the paucity of Infusoria, and the small number of aquatic 
insects enumerated are probably due to the lack of especial attention 
to these groups, such as was given: to the Rotifera. In this latter 
group 27 new species are described — the under surface of lily-pads 
having proved to be an inexhaustible source of new forms. In this 
list of Finland rotifers are to be found three species discovered by 
Jennings * in the Great Lake region of this continent. Among the 
Entomostraca Stenroos finds a seasonal polymorphism which ren- 
ders necessary a considerable reduction in the number of species in 
this group. Thus from spring to autumn Hyalodaphnia jardinii is 
successively represented by forms which have been described as 
H. obtusata, berolinensis, cucullata, kalbergensis, and autumnalis. 
Likewise in the genus Bosmina the author admits but five species, 
1 Stenroos, R E. Das Thierleben i im } aina f tatiech þi iologische 
Studie. ~ Soc. pro Fauna et Flora Soak. Bd. xvii, pp. 1-259, Taf. I-III, mit 
einer Kar 
? Jennings, H. S. A List of the Rotatoria of the Great Lakes and of Some of 
the Inland Lakes of Michigan. Bull. Mich. Fish Com. (1894), No. 3- 34 PP» 
I pl. 
