682 GARY N. CALKINS 



new one by division or by secretion. In Blepharisma the new 

 macronucleus is entirely different in texture and appearance 

 from the old and there is no doubt of its new origin. 



In Blepharisma then, we find quite a different process of 

 nuclear metamorphosis from that which occurs in the better 

 known ciliates like Paramecium or Colpidium, although in 

 essence they are the same. In Paramecium caudatum four 

 of the daughter micronuclei form four new macronuclei, losing 

 their identity as micronuclei with the metamorphosis. In 

 Blepharisma four, that is, all of the micronuclei, form macro- 

 nuclei but retain their identity within the organs which they 

 create, remaining and dividing within the macronuclear mem- 

 brane until the next following conjugation. 



Compared with the rhizopods the relations of idio- and tropho- 

 chromatin are here reversed. In the former the idiochromatin 

 is extruded from the trophochromatin or vegetative nucleus, 

 remaining in the cell body as chromidia. In Blepharisma the 

 trophochromatin is excreted from the micronucleus resulting 

 in the 'purification' of the idiochromatin which remains per- 

 manently in the macronucleus as the micronucleus. In both 

 cases it amounts to the same thing in the end, both idio- and 

 trophochromatin coming from the syncaryon, or its immediate 

 derivatives. 



It is not improbable that other forms of ciliates in which 

 micronuclei have not been observed in the vegetative stages, 

 will be found to have nuclear relations analogous to those in 

 Blepharisma. Here, also we have a clue to the explanation 

 of the nuclei of forms like Opahna where dimorphic nuclei 

 are absent. Such nuclei can be interpreted as amphinuclei 

 in which idio- and trophochromatin are not separated but re- 

 main permanently as simple nuclei. In these the idiochro- 

 matin prevails over the trophochromatin in so far as the vital 

 reproductive processes are concerned. In the majority of 

 other ciliates the dimorphic conditions are fully established, 

 an illuminating stage being seen in Blepharisma undulans where 

 the two remain together, but, nevertheless, are differentiated. 

 From such a condition to that in forms hke Paramecium is 



