Evidence front Protorionns 395 



ample, it is outside the nucleus; in Hie otlicr class it is in- 

 side the nucleus. As an exainjile of the first, several hclio- 

 zoans may be mentioned, notably Aidiithociistis and SpUnr- 

 rastrwm; and as examples of tlu- latter, several s|)ecies of 

 Cocc'idium, belonging to the Sporozoa, Knc/Irsja, a flagellate, 

 and ArceUa, a sarcodinian. Then there are combinations 

 and intermediate states between the two types. The fol- 

 lowing quotations from MInchin's book not only indicate this, 

 but bear directly on our main point. "A most instructive 

 series, showing how extranuclear elements come to collab- 

 orate in the mechanism of division, is furnished bv somi' 

 examples of the Heliozoa, and especially by the nuclear di- 

 visions of Acti7iospliaertum, which have been the subject of 

 extraordinarily thorough investigation by Hertwig. ... In 

 the ordinary karyokinesis of Actinosphaerinm an etjuatorial 

 plate is formed, composed of a large num})er of small, rod- 

 like chromosomes, imperfectly separated from one another, 

 which divide transversely. The spindle arises from the 

 achromatinic framework of the nucleus, and terminates in 

 two conspicuous polar plates lying within the persistent 

 membrane. External to the membrane are two large conical 

 masses of archoplasm, termed the 'polar cones.' " ^** In a 

 word, three distinct substances are here observed in col- 

 laboration: two, the chromatic bodies and the achromatinic 

 framework, being intra-nuclear ; and one, the archoplasmic 

 cone, being extra-nuclear. The observations indicate that 

 the archoplasmic substance is a less active collaborator in 

 the division than are the other two substances. But, })ass- 

 ing to another species, "In Actiihophrys the karyokinesis a|>- 

 pears to be of a type similar to that of Actinospluwriutn, 

 with persistent membrane, but with more activity in tlu- 

 extra-nuclear archoplasmic elements." 



And finally, relative to the degree and charactir of the 

 collaboration of the various elements: "In Arnnthort/stis, 

 however, the nuclear membrane disap})ears completely from 



