114 DAVID D. WHITNEY. 



build its framework. In all rotifers there is some skeletogenous 

 tissue and in most species the greater part of it forms the external 

 covering. In some species this external skeleton is excessively 

 delicate and flexible while in other species it is relatively thick 

 and non-flexible. This external covering is usually considered as 

 being composed of a chitinous material. In general the different 

 species of rotifers are distinguished from each other by the dif- 

 ferent forms of this external covering. If one could furnish an 

 abundance of material such as the animals use in making this 

 covering it would seem that there might be an opportunity for 

 obtaining variations in the form and size of the covering. Not 

 knowing how to obtain chitin in a liquid form other materials 

 were considered. Sodium silicate (water glass) was used first 

 and was at once successful beyond all expectations. 



Brachionus pala possesses two small posterior spines, one on 

 each side of the base of the tail, whereas the variation Brachionus 

 amphiceros not only possesses these two spines which are usually 

 longer but also possesses in addition two large lateral posterior 

 spines. These lateral spines vary somewhat in size in different 

 individuals and in the same individual they are much larger in 

 proportion to the size of the body in the young stage than in the 

 adult stage. 



During the spring and summer both forms are found but there 

 is considerable irregularity in their appearance. In the spring 

 Brachionus pala may be found almost exclusively, while later 

 Brachionus pala and Brachionus amphiceros may occur in equal 

 numbers and still later, from June to October, Brachiomis 

 amphiceros may form as high as 93 per cent, of the total collections 

 of the two forms, as was found by Kofoid. The exact cause of 

 the fluctuating appearance of these two forms in the same body 







of water is not known. 



In the first series of experiments one drop, two drops, three 

 drops, four drops, and five drops of sodium silicate were added 

 respectively to five jars each containing 150 c.c. of beef bouillon 

 culture medium. These jars were inoculated with pure cultures 

 of the green flagellate, Chlamydomonas. As soon as there was a 

 vigorous growth of the Chlamydomonas several dozen females of 

 Brachionus pala were put into each jar. After a few days had 



