Protozoa and Rotifera at Havana, III. 303 



which materially interfered with the making of full and satis- 

 factory substation lists. The first obstacle was the imperfect 

 preservation of many forms in the material put up for exami- 

 nation, the identification of this material being thus largely 

 restricted to those forms which possessed structures suffi- 

 ciently hard to preserve without distortion. The second was 

 due to changes in the list of substations under examination : 

 A and B had to be abandoned, because of extreme low water, 

 in August, 1894; Phelps Lake, in which was substation F, 

 became entirely dry by the 18th of that month, and work 

 there was suspended until January, 1895, when a rise in the 

 river refilled the lake bed; and in the spring of 1895 D was 

 abandoned and two new substations, K and L, situated in 

 Flag and Dogfish Lakes respectively, were added to the list. 

 My thanks are due to my instructor, Dr. S. A. Forbes, for 

 his interest in my work and for counsel and guidance while 

 the work was in course of preparation; to Prof. Frank 

 Smith and to Dr. C. A. Kofoid for suggestions and help in 

 technique and research ; to Mr. C. A. Hart, who has kindly 

 undertaken to revise the manuscript and prepare it for the 

 printer; and to Miss Lydia M. Hart, who has contributed the 

 figures. 



METHODS OF COLLECTION AND PRESERVATION. 



During the first season, in making collections in the river 

 and in other places comparatively free from vegetation, a tow- 

 net of No. 12 silk was used, both surface and oblique hauls 

 being taken at intervals of from seven to ten days. The col- 

 lections along shore and among plants were secured by means 

 of a Birge net, or cone-dredge, at different intervals varying 

 from fourteen to twenty-five days. Many kinds were ob- 

 tained by squeezing out the water from vegetation ; while 

 large forms, such as Megalotrocha and Conochilus, were picked 

 out with forceps and pipette. In 1896 Dr. C. A. Kofoid, 

 Superintendent of the Station, introduced the use of a pump 

 in making collections. This method has many advantages 

 over the earlier ones, as by means of it collections can easily 

 be made from any desired depth, or from among weeds where 

 a tow-net could not be hauled. 



