334 



Mr. K. B. Lewin. TJie Behaviour of the [Sept. 15, 



This caution in accepting Calkins' conclusions does not necessarily imply a 

 belief that they are incorrect. There lies, however, at the base of his reasoning 

 the tacit assumption that the micronucleus is never regenerated. Further, he 

 does not establish clearly that the micronucleus was the only organella in the 

 possession of which the regenerates differed from the merozoa which were 

 unable to recover the normal form. 



Fig. A. — Experiment on Uronychia transfuga. A, B, and A' copied from Calkins. 

 X modified from A'. 



Concerning the regeneration of the micronucleus from the meganucleus the 

 literature furnishes only the unsatisfactory note of Le Dantec ('97) which 

 states that in experiments on various mononricronucleate ciliates, not 

 further particularised, a micronucleus was found later in merozoa which had 

 been rendered amicronucleate by the operation. In no later paper does the 

 French author return to the subject, so a degree of scepticism is natural. 



I have shown (Lewin '11) that in Paramecium there occurs no regeneration 

 of the micronucleus in ordinary conditions and that the presence of this 

 organella is in no way necessary for the continuance of normal asexual life, 

 with multiplication by fission. 



Observations on Stylonychia mytilus. 



These observations are only the beginning of the complete investigation 

 that the subject demands, and are the more imperfect because of the difficulty 

 I found in keeping healthy cultures in Naples. The excellent drinking water 

 there is fatal to Stylonychia in a few hours ; boiled and aerated it varies in 

 its effects in a manner for which I am totally unable to account. 



One stock culture alone, out of many laid down, has flourished to any 

 extent, and most of my later experiments on individuals from this have been 

 entirely vitiated by the discovery of frequent nuclear irregularities. 



Methods. — Single animals were placed in a drop of the mucilage of 

 " Alga caragheen " on a slide thinly coated with paraffin. They were cut with 

 a special cutting apparatus designed for use with the system obj. A (Leitz) 



