(r 



NUCLEI IN THE MYCETOZOA. 531 



microscope we notice pairs in close proximity, often connected 

 by a bridge of nuclear matter, if we may judge from its takin 

 an equal depth of stain; this appearance is so frequently seen 

 that it is scarcely possible to be an accidental arrangement, but 

 suggests that division has occurred and that the two halves are 

 not yet entirely free. Fig. 2 a (PI. XXXV.) gives an earlier 

 stage in which two nuclei seem to be clearly united. It is in the 

 thin parts of the film, where the nuclei are flattened and the 

 plasmodic granules widely scattered, that this condition can best 

 be seen ; in deeper parts it is very difficult to ascertain whether 

 such appearances are not occasioned by two nuclei overlapping 

 at their edges. See " Additional Note " at end of paper. 



In a paper recently published in Cobn's ' Btitriige zur Biologie 

 der Pfianzen/* speaking of the plasmodiuin of Mycetozoa, Rosen 

 states : ' ; We may look in vain for nuclei caught in division. One 

 may, indeed, without great error, put down the number of nuclei 

 in a plasmodium as equal to the number of united single amcebre 

 which the plasmodium contains." 



Prom my cultivations, in which the nuclei increase in number 

 a thousandfold, it is evident that this view cannot be sustained ; 

 but Rosen's experience is interesting as showing the difficulty 

 there is in detecting the mode of increase. 



My figures are drawn from stamings made at Lyme Regis 

 in Sept. 1892, in the preparation of which my son, Mr. J. J. 

 Lister, assisted. On his return to Cambridge he made a series of 

 experiments with two species of Mycetozoa with the view of 

 finding the karyokinetic appearances described by Strasburger, 

 iollowing his method but extending his observations by noting 

 the times when the nuclear changes took place in the gradual 

 development of the sporangia ending in the formation of spores. 

 I give his account in his own words : 



" On Oct. 15, 1892, I collected a number of young sporangia 

 which had emerged from an elm-stump in the Backs of St. 

 John's College. Some of these were hardened in Flemming's 



fluid aud others were kept to ripen. When mature they were 

 identified as belonging to the species Trick ia varia, Pers. 



" On Oct. 18th a fresh crop of sporangia of this species appeared 

 on the same stump, and from that day till the 23rd I made a 

 daily gathering of sporangia and preserved them in the same 



manner. 



* Cohn, Beitr. z. Biol. Pfianzen, Bd. vi. lift. 2. Bre*lau, 1802. 



