1894.] MICROSCOPICAL JOURNAL. 259 



two flagella are sub-equal. Minute eye-like pigment- 

 specks are sometimes present, though generally absent. 

 A large vacuolar space, apparently representing a pha- 

 ryngeal dilatation, is developed at the anterior extremity. 

 The yellowish-brown color bands are produced equally 

 throughout the length of the two lateral borders. The 

 contractile vesicles are two or three in number, posteri- 

 orly located."* 



The size of the colonies varies from 30 to 75 microns 

 in diameter. Grenerally there are about twenty zooids 

 in a colony, though sometimes there are as many as 

 forty. The spherical colonies are often seen moving 

 briskly through the water with a rolling motion. The 

 elongated forms generally move more slowly. At a cer- 

 tain stage in its life history, Synura becomes encysted. 

 In this condition it is smaller in size, and the zooids are 

 crowded together and surrounded by a sheath. It is 

 also somewhat darker in color, and is entirely without 

 motion. 



Synura in its maturer condition contains oil-globules. 

 They are especially numerous just before encystment. 



At times the amount of oil has been approximately de- 

 termined. On December 9, 1893, a sample from^Basin 3 

 of the Boston water supply contained 100 colonies of 

 Synura per c.c. It had a strong, bitter taste. Each col- 

 ony had about 20 zooids, and each zooid contained about 

 20 oil-globules which had an average size of about one 

 cubic micron. Calculation showed that oil was present 

 approximately in the proportion of one part of oil to 

 25,000,000 parts of water. This seems to be a very 

 small quantity of oil to produce so strong a taste, but 

 some experiments on a few of the essential oils prove 

 that it is easily within the range of possibility. 



The following table shows the degree of dilution at 



* See Kent, loc. cit., I, 412. 



