REPRODUCTION IN THE HIGHER ANIMALS 1075 



rounded by numerous pigmented points similar to the eye- spots 

 around the natural mouth and anus, have been produced (Loeb). 



Thus, in a sense, reproduction is constantly going on within the 

 bodies even of the higher animals. But since the whole organism 

 eventually dies, as well as its constituent cells, a reproduction of the 

 whole, a regeneration en masse, is required. 



A cell of the stratum Malpighii can only, so far as we know, 

 reproduce a similar cell, and this is characteristic of cells that have 

 undergone a certain amount of differentiation, especially in the 

 higher animals. The fertilized ovum, on the other hand, has the 

 power of reproducing not only ova like itself, but the counterparts 

 of every cell in the body. And this is only the highest development 

 of a power which is in a smaller degree inherent in other cells in 

 lower forms. Plants and the lowest animals are far lees dependent 

 upon reproduction by means of special cells. A piece of a Hydra 

 separated off artificially or by simple fission becomes a complete 

 Hydra, as was shown by Trembley a century and a half ago. A 

 cutting from a branch, a root, a tuber, or even a leaf of a plant, may 

 reproduce the whole plant. It is as if each cell in these lowly forms 

 carried within it the plan of the complete organism, from which it 

 built up the perfect plant or animal. 



Reproduction in the Higher Animals. In regard to the secretions 

 of the reproductive glands, all that is necessary to be said here is 

 that, unlike other secretions, their essential constituents are living 

 cells. The spermatozoa in the male have, indeed, diverged far from 

 the primitive type. Certain cells (spermocytes) in the tubules of the 

 testicle divide, each forming two daughter spermocytes. Each of 

 the daughter spermocytes in turn divides, so that four cells (sperma- 

 tids) are formed from each spermocyte. In the final division which 

 produces the spermatids a reduction of the chromosomes (p. 1079) 

 occurs, so that the spermatid possesses only one-half the number 

 characteristic of the somatic cells of the species. The spermatids 

 elongate and become spermatozoa, the head of the latter repre- 

 senting the nucleus of the former; and it is this nucleus (with the 

 middle piece originally containing the male centrosome and attrac- 

 tion sphere) which is the essential contribution of the male to thn 

 reproductive process. The tail of the spermatozoon is simply, from 

 the physiological point of view, a motile arrangement, whose function 

 it is to carry the nucleus of the male element, freighted with all that 

 the father can transmit to the offspring, into the neighbourhood of 

 the female reproductive element or ovum. After the spermatozoon 

 has penetrated the ovum its tail disappears, being probably 

 absorbed. The function of the accessory reproductive glands, the 

 prostate, the seminal vesicles, and Cowper's gland, are not well 

 understood. But the spermatozoa in the act of. ejaculation are 

 mixed with the secretions of these glands, and therefore it is to be 



