216 A Biometrical Study of Conjugation m Paramecium 
prepared by Professor D. C. Worcester as mentioned above. In series AA pairs 
of conjugants were chosen for measurement quite at random. In the F series the 
pairs were chosen on the basis of the nuclear condition for a special purpose, and 
in a manner which will be fully described later in the paper. Regarding the 
cultural history of this material information on some particulars is unfortunately 
lacking. The reason for this is that shortly after the material was collected by 
Professor Worcester he left tlie University on an exploring expedition to the 
Philippine Islands, and, having been afterwards called to public service there, 
the work on Paramecium was never completed. His notes made at the time 
the material was collected were misplaced and cannot now be found. The most 
essential points regarding the material he was, however, able to furnish me from 
memory. For his kindness in this matter I am very grateful. His statement is 
as follows: 
The material " was obtained originally by collecting decayed cow-lily leaves 
from one of the Three Sister Lakes*. The material collected was put into stender 
dishes in the laboratory and covered in the usual way A little later an 
epidemic of conjugation started in one of the dishes. It had not progressed 
far when I discovered it, and from that time for three or four days killings were 
made at I'egular intervals, as is usually done with developing embryological 
material. I cannot state at this time just what the intervals were, but if the 
bottles in which the material was preserved still exist they ouglit to showf. 
The killings were kept up as long as there seemed to be any use in continuing 
them in order to get a complete series of specimens. The killing fluid was 
four per cent, solution of formaldehyde saturated with bichloride of mercury. 
The method pursued was to nearly fill a four-dram homoeopathic vial with 
the killing fluid and then squirt violently into it a considerable amount of 
water containing as many Paramecia as possible. As soon as the Paramecia 
had settled to the bottom of the vial the killing fluid was drawn off and the 
specimens were shaken up two or three times in distilled water, which was drawn 
off in each instance as soon as settling had taken place. They were then stained 
for twelve hours in a one per cent, solution of picrocarmine, rinsed in distilled 
water, carefully dehydrated |, and left in cedar oil, where they seemed to retain 
their colour perfectly. Mountings were ultimately made in xylol damar, covering 
glasses being supported by capillary glass rods to prevent crushing of the specimens. 
I have neglected to state that when the epidemic of conjugation began in this 
dish I drew off all available material and placed it in clear water in a smaller dish, 
for convenience in killing. In making the above statements I am, of necessity, 
trusting entirely to memory, but am very confident that they are correct." 
* Small glacial lakes in the vicinity of Ann Arbor. E. P. 
t This they unfortunately do not. K. P. 
J By a highly ingenious process which made the change to the higher grades of alcohol perfectly 
gradual and so avoided distortion from diffusion currents. To the apparatus which he devised for this 
purpose Professor Worcester's success in producing such perfect preparations as these are, was, I believe, 
largely due. K. P. 
