Evidence from Protozoavs 395 



ample, it is outside the nucleus ; in the otlier class it is in- 

 side the nucleus. . As an example of the first, several helio- 

 zoans ma}^ be mentioned, notably Acanthocysiis and Sphae- 

 rastrum; and as exam])les of the latter, several species of 

 Coccidium, belonging to the Sporozoa, Eiiglesia, a flagellate, 

 and Arcella, 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 by some 

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

 visions of Actinosphaerium, which have been the subject of 

 extraordinarily thorough investigation by Hertwig. ... In 

 the ordinary karyokinesis of Actinosphaerium an equatorial 

 plate is formed, composed of a large number 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, pass- 

 ing to another species, "In Actimophrys the karyokinesis ap- 

 pears to be of a type similar to that of Actinosphaermm^ 

 with persistent membrane, but with more activity in the 

 extra-nuclear archoplasmic elements." 



And finally, relative to the degree and character of the 

 collaboration of the various elements: "In Acanthocystis, 

 however, the nuclear membrane disappears completely from 



