THE REPRODUCTIVE ELEMENTS OF PLANTS AND ANIMALS 97 



physical forces) in certain cases overcome gravitation equally with the vital forces, but it does not follow from this 

 that gravitation as a power is extinguished. When gravitation (and this remark appUes to all the physical forces) 

 is useful in building up the organism, it is employed by nature in conjunction with the vital forces ; and when 

 capillarity, osmosis, &c., are more convenient, they are preferred. The vital and physical forces must be regarded 

 in their totality, nor must the object in view be lost sight of. Natural laws and forces (vital, chemical, and 

 physical) act and react upon each other ; and though at times some are inoperative, they are not annihilated, neither 

 are they opposed when the final effect to be produced is taken into account. Organised structures are built up in 

 accordance with natural laws. Thus, their parts and particles consist of substances which naturally have a 

 chemical afiinity for each other ; those substances absorb and respire — that is, take in and give off fluids ; they 

 exhibit, for the most part, capillary spaces and interspaces in their interior ; they have weight, porosity, elasticity, 

 and various other purely physical properties. In this way chemical affinity, osmosis, capillarity, gravitation, &c., 

 have free play, and each in turn assists not only in forming and maintaining the body, but also in disintegrating 

 it. The vital forces, if I may be allowed the expression, use and abuse the physical ones. They do not, they 

 cannot, annihilate them. As well may we say the vital forces annihilate matter. 



THE REPRODUCTIVE ELEMENTS OF PLANTS AND ANIMALS ESSENTIALLY AND 

 FUNDAMENTALLY DIFFER FROM THE BEGINNING 



Whatever may be said regarding the ultimate composition of protoplasm, the grand fact remains, that the 

 germs and seeds of plants and the eggs of animals, apparently homogeneous and identical, invariably produce not 

 only their own kind, but, during the process of development, substances which are altogether dissimilar. Even man, 

 with his wealth of imagination and thought, is the product of an egg, which to the eye of the microscopist and 

 chemist is, as to its several parts, homogeneous and identical. Yet this egg, with its several parts placed in exactly 

 the same conditions, produces the tender pulp of the brain, the fiaccid muscles, the tough tendons, the elastic carti- 

 lages, the hard bones, the stiU harder teeth, the enamel, a substance nearly as brittle as glass, and in due time the 

 several secretions, the major portion of which is composed of water. To these are to be added the external skin, 

 with its hair, nails, &c. ; the internal skin or mucous membrane, with its numerous glands ; the secreting and 

 excreting organs ; the nerves ; the lymphatics ; and the blood-vessels, with their contained blood, so rich, so 

 complex, so marvellous in composition. These various products, so diverse in form, composition, and function, 

 are, we know, the product of an egg. Shall we be told, or, if told, shall we believe, that this egg is homogeneous 

 and identical in all its parts and particles ? Identical these parts may be to the eye of sense, but to the eye of 

 reason they are not so. Matter similarly constituted, similarly disposed, and similarly conditioned — that is, placed 

 under precisely similar circumstances — behaves in precisely the same manner ; in other words, all the parts are 

 infiuenced afike. If fife had to operate on absolutely identical matter, the living mass would be simply homogeneous — 

 that is, undifferentiated ; and if undifferentiated, it would have no power to build up either a plant or an animal. 

 It is impossible to produce muscle, bone, brain, &c., from matter identical in ultimate composition. In the germ, 

 the seed, the egg, even from the first, there is differentiation, actual or potential.-' The first embryonic changes 

 are the result of this differentiation. It is this which enables the different parts of the embryo to attract and 

 assinailate different substances and to build up different tissues. One embryonic change involves another, and 

 gradually the individual is developed, each according to its kind. The weaver may not produce a web dissimilar in 

 texture and pattern in the absence of dissimilar elements. He must be supplied with the warp, the woof, and the 

 varied pigment. A queen-bee may be formed from an ordinary bee grub by changing the quantity and quality 

 of its food, but no amount of change of diet can produce from the same grub a dragon-fly or a locust. 



In making these statements regarding the non-identity of protoplasm, bioplasm, and the several parts of 



^ Mr. Herbert Spencer, in his " Principles of Biology," expressed the belief that in reproduction the cell must be regarded as the morpho- 

 logical unit, but that in addition there must be a chemical unit consisting of the simplest combination of molecules capable of displaying life. 

 Others, who regarded the nucleus as the most important part of the cell, discovered that by the employment of suitable dyes one portion of the 

 nucleus could he distinguished from all the other parts. This they designated the chromatin. The chromatin, it was found, could he broken up into 

 a number of rod-like bodies, which were designated chromosmies. The chromosomes, when stained, were found in turn to be compound and 

 divisible into microsomes. This much could be demonstrated by the aid of the microscope with stained nuclei : when its powers failed, Professor 

 Weismann, by a process of reasoning, inferred that each of the microsomes consisted of a number of still smaller bodies, which he called determinants. 

 The determinants Weismann regarded as the structures forming the germ-plasm which decided the nature and character of the adult organism. 

 Weismann went further, and assumed that not even the determinants constituted the ultimate living elements. The detei-minants, he believed, 

 were further resolvable into biophores. Weismann, who has done much to expiscate this most involved and diihcult subject, was by no means the 

 first to deal with it in a more or less exhaustive manner. It has been a veritable bone of contention for over thirty years — each author employing 

 his own nomenclature. 



From the foregoing it will be seen that the reproductive cell is by no means a simple structure, and that it is seen to be more complex in 

 proportion as our opportunities gf investigating it inoreas?, 



VOL. I. N 



