The President's Address. By the Rev. W. H. Dallinger. 201 



lens must be brought into action ; and, as all manipulators and 

 experts in the use of high-power lenses know, this is dependent 

 upon careful centering and a delicate facility and power in the use 

 of light. But exaggerated results that, although not to be relied 

 on at all by themselves, are none the less valuable in a high degree 

 as ancilliary means, may be obtained by the judicious use of acetic 

 methyl-green. 



It will sujSice for my present purpose if I give you the details 

 in two cases. In none are they more beautiful than in Tetramitus 

 rostratus and Dallingeria Drysdali. I have already pointed out 

 that the nuclei of these forms differ considerably in size. In the 

 selection of the two I have named we have one of the largest, and 

 although not the smallest, still a relatively very small one, if we 

 take the group as a whole. The nucleus of Tetramitus rostratus 

 averages the 1/10,000 in. in length ; that of D. Brysdali ave- 

 rages the 1/20,000 in. For several reasons I give the results 

 of examination with the same lenses, and the same magnifying 

 power. If we examine B. Drysdali first, we shall see the pro- 

 blem in its most difficult form, and shall be the better able to 

 appreciate the identity of behaviour in the nuclei of both. Indeed, 

 in each of the four nucleated forms, if steadily followed from the 

 time that they have attained maturity from the germ, it will be 

 seen that the plexus-like state of the nucleus is being lost in 

 certain parts of it, that is to say, that the plexus-like structure 

 which had become diffused over the entire hyaloplasm of the 

 nucleus, aggregates in definite parts, leaving other parts absolutely 

 clear and transparent. In the case of D. Drysdali, it is the loiver 

 part of the nucleus that becomes thus hyaline. 



On close examination and with carefully managed light, it 

 may be seen with the 1/20 of 1*5 N.A., and with the 1/50 of 

 1 • 38 N. A., as drawn in plate VIII. fig. 7, where at a, a, a, a portion 

 of the general somatic sarcode is seen, and at h the nucleus. Instead 

 of the plexus-like structure being found everywhere in the nucleus, 

 as it was in fig. 3 ibid., it is wholly wanting in that part of the 

 nuclear body marked c, and is much denser than before in the 

 part marked b. In this condition not a trace of fissional action is 

 to be seen in the general substance of the body, nor any of its 

 parts: but if the observation be continued it will be seen that 

 there rapidly appears in the long axis of the nucleus, at first 

 faintly then more clearly, a bead-like line seen at d, fig. 8, and two 

 or three finer threads run from the plexus-mass e to this middle 

 line. At this point it is that a minute disparting of the nucleus 

 occurs at the point d, so slight as to require great care in observa- 

 tion, and this is immediately followed by a slight white line d e, 

 resulting in the first incision of the body-substance as at /. The 

 white line now widens, and extends the whole length of the body 



