148 CHROMOSOMES IN THE -SPERMATOGENESIS OF THE HEMIPTERA HETEKOPTERA. 



reduction division, which is a division breaking the Hnin connections between con- 

 jugated chromosomes, its later reconstitution, i. e., the restoration of a nuclear con- 

 tinuous nuclear element in the next generation, must take place by the maternal and 

 paternal chromosomes arranging themselves in a continuous chain in such a way, that 

 every two correspondent paternal and maternal chromosomes lie together. For this 

 alone would explain why chromosomes of corresponding appearance are placed 

 together in the prophases of division, and how in the synapsis stage of the growtli 

 period corresponding chromosomes conjugate unerringly. 



The main results of these observations and interpretations amount to this, that 

 the important nuclear element of the first order is a continuous band of linin with 

 which chromatin is always locally connected. Beyond this there is in the nucleus 

 nothing but the karyolymph, the nucleoli (plasmosomes), and minute floating gran- 

 ules (cedematin or lanthanin). With considerable justification we may assign to this 

 nuclear element the main activities of heredity and differentiation, because it is the 

 most constant structure. 



Therefore we are to conceive of chromosomes not as separated nuclear masses, but 

 as bodies in continuous physical connection. And each chromosome is a mass not of 

 chromatin alone, but of chromatin always combined with linin, whether the chromatin 

 be condensed as in mitosis, or whether it be finely distributed along delicate linin 

 fibrils as in the rest stage. These two substances must be considered conjointly in any 

 concept of the " hereditable substance," and not, as so many seem inclined to do, only 

 the chromatin. 



As elements of a second, lower grade we find the chromosomes. And we may 

 define chromosome as a particular portion of the nuclear element on which the chro- 

 matin becomes massed during cell division. We can imagine the relation most 

 simply in this way : there is a continuous linin band, on which chromatin is always 

 suspended, more or less sparsely and irregularly when the cell is not in division, but 

 in compact masses during division ; each portion of a linin band on which chromatin 

 is so massed in division is a chromosome. Whether the movement of the chromatin 

 particles on this band is automatic, or whether it is produced by local contractions of 

 the linin, we have no means of deciding ; but certainly it is independent of extra- 

 nuclear energies. 



This idea of mine of the chromosomes as mere portions of a continuous nuclear 

 element by no means implies that the cbromosomes are not to be considered indi- 

 viduals, i. c, structures that reappear in the same form and number in cell generation 

 after generation. Indeed there is as much evidence that each chromosome is the prod- 

 uct of a preceding one ami not a new formation, as that a cell is always the division 



