392 PKOF. ALLMAN O^ THE RECENT EESEARCHES 



regarding the condition of the nuclei ; nor were they able to folloAV 

 the process through any further stages. 



They have also studied a phenomenon which has been regarded 

 by other observers as a conjugation of two individuals, but which 

 Ilertwig and Lesser interpret as a case of reproduction by spon- 

 taneous division. In this the appearance presented is that of two 

 indi\T.duals in union with one another by their pseudopodial sur- 

 faces, where they are connected by a broad bridge of protoplasm, 

 which stretches from the soft body of one animal to that of the 

 other. One of these connected individuals has always the usual 

 dark brown shell, while in the other the shell is clear and colour- 

 less. Across the connecting bridge the protoplasmic contents of 

 one shell pass over into the other until the former is nearly 

 emptied. Then the direction of the stream is reversed and the 

 nearly emptied shell becomes filled at the expense of the other. 

 This interchange of the contents now repeats itself, and thus goes 

 on rhythmically for some time, when a period of rest sets in, the 

 protoplasm bridge becomes gradually thinner, and finally breaks 

 across, and the two hitherto united ArcellcB become detached from 

 one another, each composed of nearly an equal part of the origi- 

 nally single protoplasm mass, which, according to the interpre- 

 tation of Hertwig and Lesser, has thus become divided into two 

 independent segments. 



Biitschli has described in Arcella a somewhat difibrent pheno- 

 menon, which he regards as a true conjugation*. In this three 

 individuals, all with dark brown shells, were observed to be in union 

 with each other by means of bridges of protoplasm which pro- 

 ceeded from the sheU-orifices. On the day following the separa- 

 tion of the conjugating ArcellcB he noticed that in one of the in- 

 dividuals the protoplasm-body had withdrawn itself for a consi- 

 derable space from the shell-wall, and that in the liquid which 

 filled the interval a multitude of Fi'Srio-like bodies swarmed, while 

 in close contact with the dorsal surface of the protoplasm there 

 lay numerous flat disk-shaped masses of protoplasm. After some 

 time these showed lively amoeboid movements, and crept about be- 

 tween the body of the parent animal and the shell-walls. These 

 amoeboid bodies ultimately crept out through the shell-orifice. 

 They contained a contractile vacuole and a clear nucleus, and moved 

 by the protrusion of short very blunt processes. Biitschli was 

 not able to follow their further development ; but he does not hesi- 

 * Arch. f. niikr. Anat. vol. xi. (1875) p. 459, pi. xxv. 



