No. 3-] MORPHOLOGY OF THE STENTORS. 513 



nucleus, always parallel to the long axis of the animal (Fig. 

 41 d, e,f). As soon as elongation has begun, a constriction 

 appears about the nucleus, and persists for about half-an-hour 

 (Fig. 41 b-c). In less than an hour the nucleus attains a 

 slender, rod-like form (/, g, h), normally straight and cylin- 

 drical, but almost invariably bent or curved by the occasional 

 contractions of the animal, as seen in Fig. 41 g, h, i. The 

 meganucleus, however, always tends to straighten, and will do 

 so if the intervals between contractions be sufficiently long. 



When elongation has reached its limit, and sometimes per- 

 haps even before, nodes appear at the tips of the meganucleus 

 (Figs. 35, mgn.\ 41 i). I have found no exception to the rule 

 that the nodes develop first at the ends of the meganucleus. 

 The nodulation advances rapidly and at nearly equal rate 

 towards the middle of the nucleus, so that at any stage in the 

 process one counts about as many nodes in one moiety of the 

 nucleus as in the other; but there is usually a difference of 

 one or two (Figs. 35, 41). The nodulation soon reaches the 

 middle point of the nucleus, which normally lies in the plane 

 of the constriction between the now nearly-divided daughter 

 stentors. The newly-formed nodes are, as a rule, beautifully 

 symmetrical and alike in size. As soon as the nucleus has 

 become fully-noded, the middle commissure, lying just opposite 

 the fission-line (Fig. 42) at once becomes longer and finer than 

 any of the others. It differs from all the other commissures in 

 being a commissure of division, comparable to the connective 

 uniting the moieties of an amitotic nucleus. Rupture of the 

 commissure takes place shortly before the separation of the 

 daughter-stentors (Fig. 43), and the "tail-ends " at the adjoining 

 tips of the meganuclei are speedily drawn into the terminal 

 nodes. 



The way in which nodulation takes place is worthy of note. 

 The first thing observable is a series of constrictions, all of 

 nearly equal depth and evenly spaced. At this early stage a 

 stained preparation, such as Fig. 44 represents, shows that the 

 chromatic substance has become aggregated in the incipient 

 nodes, and the commissures are nearly destitute of it. Thus at 

 the outset the commissures are relegated to the comparatively 



