The Sponges of Lake Biwa. 3 



Description of the Species. 

 Genus Spongilla, Lamarck. 



Subgenus Euspongilla, Vejdovsky. 



SpoHfßilla lacustris, auct. 



PL I, Figs. 1—3. 



1909, Weltner, Brauer's Süsswasserfauna Deutschlands XIX, p. 181, figs. 301, 304-309. 

 1909, Annandale, Proe. U. S. Nat. Mus. XXXVI, p. 631. 

 1915, Annandale, Mem. Ind. Mus. V, p. 26. 



This sponge is one of the most widely distributed and the most 

 plastic of the Spongillidae. It is also probably the most primitive 

 in essential characters. Numerous varieties have been described, 

 and it is doubtful whether some of the forms at present recognized 

 as allied species are really distinct specifically. It is very difficult 

 in any case to draw up a diagnosis that will exclude all such forms. 

 The following description will be useful at least in distinguishing 

 the species from the other Japanese Spongillidae. 



The sponge is as a rule soft and fragile. It has, when grow- 

 ing in a good light, a bright green colour, which is due to the 

 presence within the cells of its parenchyma of a minute unicellular 

 Alga (Chlorella) ; in a faint light the green colour sometimes 

 disappears, but in this condition the outlines of the capsules of the 

 symbiotic alga can still be detected. 



The typical form of the species is that of a thin encrusting 

 layer from which vertical branches, elongate, slender and cylindrical, 

 arise, but it may be massive without branches. The branches may 

 be flattened instead of cylindrical and they may anastomose so as to 

 form a complicated network. On the other hand the sponge may 

 be reduced to a thin film of a small area. 



The oscula as a rule are not very conspicuous, but they may 

 grow large and have well-defined borders. In the living sponge 

 they are protected by transparent "collars" of a conical form. 

 The external (i. e. subdermal) terminations of the main exhalant 

 canals (which are commonly confused with the dermal pores or 

 ostia) are never very large or conspicuous. 



