748 CALKINS. [Vol. XV. 



In the second place, during the anaphase ' the chromatin-loops 

 become reduced to thick threads and the ' Polkorperchen ' is 

 redrawn into the nucleus.' Finally, after the stage just 

 described, the chromatin regains first its coarse and then its 

 fine mesh-like structure, and the ' nucleolus ' reappears in the 

 nucleus. If the ' Polkorperchen ' is withdrawn into the nucleus, 

 and if the nucleolus reappears shortly afterwards, it is probable 

 that the ' nucleolus ' is derived from the pole-bodies. Also, if 

 the ' nucleolus ' is thus derived from the ' Polkorperchen,' and if 

 it disappears when the new pole-bodies are formed, an equally 

 possible inference is that the pole-bodies are actually derived 

 from the ' nucleolus.' " There is reason, therefore, to believe 

 that in EuglypJia, also, the "achromatic bodies" are intra- 

 nuclear in origin. 



The nuclear division of Spirochona was first described by 

 Hertwig ('77). Since then it has been described by a number 

 of observers, Balbiani ('95) being the most recent. Hertwig 

 describes the resting-nucleus as consisting distinctly of two 

 parts, one finely granular, and the other homogeneous in 

 structure. Balbiani ('95) has, in the main, confirmed Hertwig's 

 description of the Spirochona resting-nucleus. He finds, how- 

 ever, that the two parts of the nucleus are separated by a 

 fissure or "fente," which he thinks is the " Kernspalt " of the 

 ciliate macronuclei. The " homogeneous " part, which undoubt- 

 edly corresponds to the "achromatic body" of other Protozoa, 

 is, therefore, within the nuclear membrane, but, as in Noctilitca 

 and Parmnocba, it is completely separated from the chromatin. 

 Hertwig describes a small central granule in the homogeneous 

 part, while Balbiani's description shows that other structures 

 of a fibrous nature are also present before this body appears. 

 He finds in stained preparations that the achromatic part 

 (which appears homogeneous during life) contains numerous 

 short fibers which form a network. These fibers do not stain 

 with ordinary chromatin dyes and become arranged in a certain 

 definite manner about the " nucleolus " (central granule in the 

 "homogeneous" or achromatic body), which appears later. ^ 



1 " La partie dite homogene du noyau ne merite pas non plus cette qualification 

 dans le noyau fixe par les reactifs. EUe aussi presente un continu filamenteux 



