386 CALKINS. 



atively thick shell and is provided with fine, needle-like spines 

 (Fig. I 2). Variety B has a collar bearing six distinct spikes on 

 its outer margin. Its wall is comparatively thin and is pro- 

 vided with spines of thorn-like structure, /. c, with broad bases 

 and sharp points (Fig. 13). In both cases the protoplasm is 

 characterized by great vacuoles in which lie a varying number 

 of plastids. The nucleus in variety A resembles that of T. 

 lagenella in having an irregular mass of chromatin granules. 

 The edge of the mass is irregular and more or less ** frayed 

 out," leaving little doubt as to the absence of a nuclear mem- 

 brane. The central body is comparatively small and is either 

 round or elliptical in form. The nucleus of variety B, on the 

 other hand, presents quite a different appearance. It is very 

 regular in outline, the margins are smooth and even, and a deli- 

 cate though distinct membrane encloses it. The central gran- 

 ule is large and conspicuous (Fig. i 3). 



In Trachelomonas volvociiia the nucleus resembles that of T. 

 liispida variety B. The cell is somewhat more compact how- 

 ever, the nucleus is smaller and the cytoplasm contains more 

 plastids (Fig. 14). 



Eiiglena viridis (PI. XXXV, Figs. 17, 18, 19). Euglena, 

 of the same family as the Trachclomonads has, perhaps, the 

 most highly differentiated nucleus of the intermediate type. 

 Blochmann ('94) and Keuten ('95) described this nucleus as 

 a group of chromatin granules enclosed by a membrane, and sur- 

 rounding a central body — the ** nucleolus-centrosome." Each 

 chromatin granule was described as a '' Stcibchen'' or rod-like 

 element. Biitschli ('90) had described, in addition to the chro- 

 matin granules and central body, a more or less distinct linin 

 network which was apparently overlooked by Keuten. This 

 so-called linin substance is extremely difficult to see but in thin 

 sections and with the use of oblique light can be made out as 

 delicate fibrils running from granule to granule. This structure 

 could not be seen in the shelled euglenoids (Trachelomonas)^ pos- 

 sibly because the nuclei were not so easy to study, being total 

 preparations of shelled forms. In other monads, as for example 

 C/iilojuonas, which are as easy to study in total preparations as 



