April, 1911. 



KNOWLEDGE. 



153 



organism, there is found a certain amount of a substance 

 remarkable for its affinity for certain colouring matters, and 

 still more remarkable for the part it plays in all vital processes. 

 From the first of these characteristics the name chromatin has 

 been given to it. It is a substance, or combination of 

 substances, of a very high degree of chemical complexity, 

 perhaps more complex than any other substance, but it is by 

 no means of uniform chemical composition. The term 

 chromatin implies, in short, a biological or physiological, but 

 not a chemical, unity. 



In the lower type of Prutist organisation, which is exem- 

 plified by the ordinary Bacteria, the chromatin is present in the 

 form of scattered granules — "chromidia." In the second type 

 a certain amount of the chromatin may still be present in the 

 scattered chromidial condition ; but the greater part, and in most 

 cases all of the chromatin, is aggregated into a compact mass, 

 the nucleus, and. apart from this nucleus, the remainder of the 

 living body is made up of a distinct protoplasmic zone — the 

 cytoplasm, scarcely recognisable in the bacterial type. With 

 difterentiation of nucleus and cytoplasm, the organism becomes 

 a "cell." This type will be termed the "cellular grade." 

 Reference was then made to 

 the existence in all forms of 



higher life of sex and sexual N^ 



differentiation, and even in 

 the Protista we find sexual 

 phenomena to be of uni- 

 versal occurrence in the 

 cellular grade, but quite 

 absent in the organisms of 

 the bacterial grade. Much 

 has been written, and many 

 theories put forward, to '^»v^ 



explain the origin and sig- 

 nificance of sex. Professor 

 Minchin dealt briefly with 



only one, that put forward by Doflein. and founded 

 by him on those enunciated previously by Hertwig 

 and Schaudinn. This theory is, shortly, as follows : — Living 

 cells are regarded as consisting of two groups of vitally active 

 substances, the one regulating motor, the other trophic, 

 functions. In cell-reproduction by fission, these substances 

 are never distributed with mathematical equality amongst the 

 descendants ; hence continued reproduction of this kind brings 

 about accumulations of different properties in certain 

 individuals, with, as a consequence, impaired vital activity and 

 reproductive power. Individuals are produced, some of which 

 are richer in stored-up nutriment (female), others in motile 

 substance (male). Since these two kinds of individuals contain 

 aggregations of substances which have intense nmtual chemical 

 reactions, they exert an attraction one towards the other ; the 

 two individuals tend to unite, and by their union cell-equilibrium 

 is restored and vital powers renewed. Hence syngamy is 

 regarded as a necessity for the life-cycle, due primarily to the 

 imperfections of cell-division and to the consequent loss of 

 equilibrium in the cell-constituents. On this view, the general 

 absence of sex phenomena in the lowest grade, and its existence 

 in the higher, is readily intelligible. In the bacterial grade, the 

 body, usually very minute, is of extremely simple structure. 

 In such organisms, inequalities of cell-division, if they occur, 

 can be adjusted easily by the rearrangement of the chromatin 

 substance. On the other hand, with the evolution of the 

 cellular grade, the body is differentiated into at least two parts, 

 nucleus and cytoplasm, and becomes of increasingly complex 

 structure. Consequently, an exact quantitative and ijualitative 

 partition of the body during cell-division is of extremely im- 

 probable occurrence — at least, until the mechanism of cell- 

 division has reached its greatest perfection. The fact that in 

 the Infusoria, the most complex in structure of all the Protista, 

 syngamy is a frequent event and easy to observe, fits in also 

 with the view that sex phenomena are in relation to complica- 

 tion of cell structure ; and, conversely, the fact that in 

 Protozoa of simple structure, such as the Flagellata, syngamy 

 is rarer, and appears only to occur at long intervals in the Ufe- 

 cycle, also receives a simple explanation. From all these facts 



Figure 1. 

 and 



and considerations, it appears extremely probable that sex and 

 syngamy were "invented" when the cellular grade was evolved 

 from the b.acterial grade of structure. This, again, the speaker 

 said, is related to another very important property of living 

 things — the more or less easy divisibility into groups which we 

 now term species. No one now considers a species as a fixed 

 and immutable entity. Nevertheless, the fact remains that 

 the tendency of living things to separate themselves into species 

 more or less distinct is one of the most constant and universal 

 pecularities of the organic world. 



From these consider.ations it is evident that the passage 

 from the bacterial to the cellular grade was, perhaps, the most 

 important advance in the evolution of living beings. The 

 acquisition of the cellular type of structure was the starting- 

 point for the evolution, not only of the higher groups of the 

 Protista, but. through them, of the whole visible everyday world 

 of animals and plants, in all of which the cell is the unit of 

 structure, and which consists primarily of aggregates of cells. 

 Further.with the cellular type of structure were initiated, in the 

 speaker's opinion, two of the most universal and characteristic 

 peculiarities of living beings — namely, the phenomena of sex 



and the tendency to form 



species. 



AN INTERESTING 

 MICRO -OBJECT FROM 

 A SINGULAR SOURCE. 

 — The fungus known popu- 

 larly as the truffle, and used 

 as a flavouring, affords some 

 interesting and instructi%e 

 microscopical objects. At 

 the same time it is not 

 exactly easy to obtain, 

 and it occurred to me 

 to resort to the " truffle 

 liver sausage," so nuich in evidence at the foreign 

 " dclikatessen " shops, frequently found in some parts of 

 London. The result was perfectly satisfactory ; a thin 

 slice of the delicacy yielding ample material for examina- 

 tion, and for mounting hundreds of slides had such been 

 desired. 



Several different species of the famil\' Tiibcraceae do duty 

 as " truffles " in the popular sense, nor do the\' differ much 

 from one another in character. As their name implies, they 

 bear an outward resemblance to a tuber, such as a small 

 potato or artichoke. Inside they are composed of liyphae — 

 the much-branched and anastomosing tubular threads — which 

 make up the greater part of all fungi. These are packed closely 

 together, but numerous spaces and channels are found in which 

 on the ends of the hyphae are developed the asci, or spore sacs. 

 In most members of this family these are more or less spherical 

 and contain typically four spores. In my specimen the bundles 

 of hyphae are of a grayish tint, while the intervals with the 

 numerous sacs containing brown, almost black, spores show as 

 a darker mottling on the ground mass as represented in Figure 

 la, which is a portion only slightly m.agnified (about X 5). 

 There may be from one to four spores in an ascus and they 

 are not formed simultaneously (Goebel), so that under the 

 microscope, while one may be fully developed, others show 

 earlier stages. The outer coat of the mature spore is thick and 

 strongly cuticularized and is ornamented throughout the family 

 with projections of various kinds. In the present species the 

 large and handsome spores are covered with sharp spikes and 

 points, Figure lb. A second thinner coat within is easily made 

 out with careful focussing. The young spores have less colour, 

 and according to age the characteristic markings of the outer 

 coat are not so fully developed. As in most of the very large 

 class of ascomycetous fungi, the asci are elongated tabular 

 sacs, while the typical number of spores in them is eight, 

 — though exceptions are not few — the family brought under 

 notice forms an interesting variety for comparison ; while also 

 many of its life processes, such as to some extent its method of 

 growth from the spores and details of the formation of its 

 fructifications, are still unkriown. J. B. 



