ESSENTIAL FEATURES OF SEXUAL PROCESS 1347 



others are subordinated to the metabolic needs of these germ-cells and are 

 transformed into various elements, such as nurse-cells, wandering mesoderm 

 cells or phagocytes, yolk-cells, and so one. Gaskell regards the greater part, 

 if not the whole, of the connective -tissue framework of the body, as well as 

 the wandering corpuscles of the blood and tissue-fluids, as derived from these 

 primitive germ-cells. All these tissues, though useful to the host as well as 

 to the finally successful germ-cells, present the common feature of an absolute 

 independence of the central nervous system. Thus the evolution of the animal 

 kingdom means essentially the evolution of the host, and must therefore be 

 closely connected with the evolution of the central nervous system, the ruling 

 element in the neuro -muscular syncytium. On these grounds Gaskell has used 

 the comparative morphology of the central nervous system as a means of tracing 

 the origin of the vertebrate from the invertebrate type, and has come to the 

 conclusion that the immediate ancestor of the vertebrate must be sought in 

 the invertebrate group presenting the most highly developed central nervous 

 system, namely, the arthropoda. 



The whole of the complex mechanisms which are concerned in 

 maintaining the life of the individual have apparently been developed 

 in order to give the potentially immortal germ-cells a better chance 

 of survival in the struggle for existence. From the broad biological 

 standpoint, as Foster points out, all the toil and turmoil of human 

 existence may be regarded simply as the by-play of an ovum-bearing 

 organism. From the same standpoint one must acknowledge that 

 the mortality of the individual, resulting from the absence of an 

 indefinite power of multiplication among the somatic cells, must be 

 an advantage to the race. Throughout the living world the welfare 

 of the individual is subordinated to that of the species. With each new 

 generation there are possibilities of variation and of the production 

 of individuals better or worse fitted for the maintenance of the race 

 than those of the previous generation. Immortality of the indi- 

 vidual would handicap the survival of the younger generations, and we 

 should have the same retardation of progress in a race that we see 

 in many civilised communities, where the power and the conduct of 

 affairs are in the hands of the older members. 



THE FORMATION OF GERM-CELLS 



In multicellular organisms the cells which conjugate to form a new 

 cell, capable of developing into an individual, are of two kinds. One, 

 which has generally a certain amount of reserve material stored up in 

 its cytoplasm, is the female element and is called the ovum. The other 

 cell, which consists of little more than nuclear material, is the male 

 element and is called the spermatozoon. Both kinds of cells are 

 derived from a mass of undifferentiated cells, the germ epithelium, 

 which, as we have seen, can often be traced directly back to the first 

 divisions of the fertilised egg. The use of the reserve material in the 

 ovum is to serve as food for the developing individual. The ovum 



