THE ULTIMATE SEX-ELEMENTS. 87 



embryologists call the blastoderm was more than incipient, two cells 

 were observed to be set apart externally. (These had nothing what- 

 ever to do with the polar globules seen in most ova at maturation.) 

 The development proceeded apace, but the isolated cells took no 

 share; they may be presumed to have retained intact the characters 

 which they received when first divided off from the ovum. At a 

 certain stage, however, the insulated cells sank inwards, took up an 

 internal position, became the rudiments of the reproductive organs. 

 Here, then, at an early stage, before differentiation is marked, the 

 reproductive cells are set apart. They must therefore preserve much 

 of the character of the parent ovum, and hand on the tradition intact 

 by continuous cell -division to the next generation. 



In other words, in the preceding case, at a very early stage in the 

 embryo, the future reproductive cells are distinguishable and separable 

 from the body-forming cells. The latter develop in manifold variety, 

 into skin and nerve, muscle and blood, gut and gland; they differ- 

 entiate, and lose almost all protoplasmic likeness to the mother ovum. 

 But the reproductive cells are set apart; they take no share in the 

 differentiation, but remain virtually unchanged, and continue unaltered 

 the protoplasmic tradition of the original ovum. After a while they, 

 or their division-products rather, will be liberated as reproductive 

 cells. These in a sense will be continuous with the parental germ. 

 Their protoplasm will be more or less identical. The original ovum 

 has certain characteristics, a b c ; it divides, and all its cells must at 

 first more or less share these characteristics; the body-cells lose them, 

 the insulated reproductive cells must retain them. The ovum of the 

 next generation has thus also the characteristics a b c, and must there- 

 fore produce an organism essentially like the parent. 



An early isolation of the reproductive cells, though never so strik r 

 ing as in Chironomus, has been observed in many cases, — for exam- 

 ple, in other insects, in the aberrant worm-type Sagitta, in leeches, in 

 threadworms or nematodes, in some Polyzoa, in some small crusta- 

 ceans known as Cladocera, in the water-flea Minna, and in some 

 spiders (Phalangida), and probably in other cases. As the series is 

 ascended, the reproductive organs are later in making their appear- 

 ance, or at least they are only detected at a later stage; and it must 

 also be pointed out that, in cases of alternation of generations, an 

 entire asexual generation, or more than one, may intervene between 

 one ovum and another. 



VIII. Body-cells and Reproductive Cells. — Various natural- 

 ists have insisted on the contrast hinted at above, between the cells 

 of the embryo which go to form the body, and those which are set 

 apart as reproductive organs. 



