468 THE AMERICAN NATURALIST [Vol. L VI 



opcniii- of the shell and a new shell being formed oyer the ex- 

 ])osed part of the body, the two shells, old and new, lyino; mouth 

 to montli. The body then divides and the new Individual 

 moves away to lead a separate existence. 



At times two Difflugias have been observed attached mouth 

 to mouth and have been thoufrht to be conjugating. When di- 

 viding the new shell is much lighter in color than the old and 

 in the ca.es supi)osed to be conjugating both shells were of the 

 same shade, that is both dark,, so that the phenomenon did not 

 seem to be that of division. Tt was this attachment or so-called 

 conjugation which I endeavored to investigate. 



It w^as found by Dr. Jennings (not published as far as I am 

 aware) that two Difflugias could sometimes be made to attach 

 tiiemsclves together by keeping them in a drop of distilled 

 water for a few hours. At his suggestion, I used this method, 

 endeavoring to hasten the process somewhat by pushing the 

 individuals together by means of a fine glass rod. In several 

 cases, the members of the pair became quite firmly united and 

 remained so for some time. These pairs I then put into a drop 

 of culture medium in the concavity of a hollow ground slide. 

 In some cases such individuals never separated but died. In 



[Ji-irfly. i.i-i;ecdut.' tlnMi was this. The number of spines 



3. s(.metinu-> as lunh a- (i. Tli.- .i/c of the shell also varies. 

 I used the diamrtu- acn ss Wu- ^^uU■.\ part of the shell. I se- 

 lected, for exaiiiplc. a small individual with a few spines and 

 kept it under (.hsfi-vai loii on a hollow ground slide in culture me- 

 dium until it had produced an ott'spring by division. (The cul- 

 ture mrdiuni eonsisted of tap water containing the microscopic 

 drbris ^^a^l^■.l fn m the leaves of Ehulea.) I then isolated the 

 oft'spring and allowed it to produce a race, keeping each indi- 

 vidual separate on a slide, and nn"a>uring and counting the 

 number of spines of each. Th,. ori-inal l)iflln-ia 1 Iri.'d to 



which had previously i.roducMl an .^rNprin- uhieli I h.ad iso- 

 lated and allowed to found a lac'. if ;ln' hn-'v and Muall Dif- 



cessfully separated. I ilion isolated each one on a slulf and al- 

 lowed each to .start a line of prou'eny. L then had 4 lines 

 going, one from each Difflugia before conjugation and one from 



