ZOOLOGY AND BOTANY, MICROSCOPY, ETC. G31 



up as such, but that the primitive elementary parts are convertible 

 at any time. Other infusorians did not give as striking results as 

 Stentor cseruleus, but Dr. Gruber thinks that the difference depends 

 on the greater or less faculty of existing under conditions which are 

 not quite natural, and that the power of replacing lost parts is proper 

 to all Protozoa. This remarkable acquisition of the regenerative 

 faculty may depend on the fact that Protozoa frequently break up 

 spontaneously into irregular fragments, and that many of these frag- 

 ments are capable of again being developed into normal animals. 



The author next proceeds to discuss the significance of the nucleus 

 in regeneration ; the want of the nucleus brings about an incapacity 

 to replace lost parts, or produce new structures, and it is clear that 

 the nucleus is the most important, and the species-preservative con- 

 stituent of the cell, and to it we justly ascribe the highest importance 

 in the processes of fecundation and inheritance. A study of Amoeba 

 binucleata showed that though the chromatic substance of the nuclei 

 varies considerably in form and arrangement, the true nuclei of any 

 one specimen always agree ; this seems to show that the chromatin 

 in the nucleus is an important factor and is not merely an accumu- 

 lation of nutritive material. 



The observation of the phenomena of spontaneous division led to 

 the discovery of certain small differences between the daughter- 

 individuals, and this appears to indicate that the morphological and 

 physiological congruency of the two daughter-individuals produced by 

 division is by no means quite absolute. In Stentor division ordinarily 

 took place at intervals of two days, and the presence or absence of 

 nutrient material had no influence on the time of tho division. Of 

 this spontaneous division two kinds may be distinguished among 

 Infusoria ; one occurs when the individual has grown to a certain 

 size which cannot be exceeded ; the other is by divisions follow- 

 ing on one another rapidly, and in definite intervals of time, without 

 intervening growth ; this, of course, is combined with continual 

 decrease in the size of the body, and happens wheu tho infusorian is 

 placed under unfavourable conditions, in which it is desirable to 

 rapidly produce a large number of individuals for the preservation of 

 the species. These hurried divisions are succeeded by a period of 

 conjugation. 



The behaviour of infusorians during conjugation throws some 

 light on the nature of the nervous elements in the cell ; as Gruber 

 has already stated, the two members of a pair in copula make exactly 

 concordant movements so long as they are still united by a bridge 

 of protoplasm. As a single thread-like bridge of protoplasm suffices 

 to cause the loosely connected pieces to behave as one individual, it 

 is clear that the nervous functions in the infusorial body are not 

 confined to definite courses, and that the exertion of will uniformly 

 governs every protoplasmic element. In other words, the nervous 

 potency of the cell is diffused. The consentaneous action of the 

 individuals of a protozoic colony is due to the fact that they are united 

 to one another by cords of protoplasm. The seat of the diffused 

 nervous potency is chiefly to be sought for in the cortex. 



