The spermatogenesis of Peripatus (Peripatopsis) balfouri. 349 



spirem probably persists. In the rest and in mitosis the chromatin 

 is placed on or in this spirem ; in the rest stage the spirem appears 

 to give out delicate branches, and on these too the chromatin may 

 be arranged. There is no evidence that any chromatin is disassociated 

 from this linin spirem. Thus the whole, the linin spirem with the chro- 

 matin arranged within or upon it, may be said to constitute a single 

 element of the nucleus, distinct from the caryolymph and true nucleoli 

 (also from the lanthanin granules and their supporting networks?), to 

 which may be applied the term "nuclear element". This is an indi- 

 vidual of the first order. As individuals of a second, lower order, may 

 be regarded its component chromosomes. But the nuclear element is 

 made up not only of chromosomes but also of inter-chromosomal linin 

 fibres though these become part of chromosomes (i. e. covered with 

 chromatin) whenever a continuous chromatin spirem is produced. Now 

 my observations show that not only is the higher individual, the nuclear 

 element, but also the individuals of lower order, the chromosomes, are 

 structures which persist from generation to generation. My observa- 

 tions show that the univalent chromosome in one generation is made 

 up of the same chromatin and linin connections which it had in the 

 previous generation: and the individuality is retained apparently by 

 virtue of the persisting linin connections ^). 



In spermatocytes of the first order the chromosomes are bivalent, 

 each bivalent chromosome in Peripatus being composed of two axial 

 linin threads with their chromatin, and also of an inter-chromosomal 

 fibre (central thread) which joins the two central ends of the two 

 univalent chromosomes. Such a bivalent chromosome seems to be found 

 only in spermatocytes and ovocytes, is an individual of a higher order 

 than the univalent chromosome, and also preserves its individuality 

 throughout the rest stage. 



1) Rabl (1885) is the founder of the theory of the individuality 

 of the chromosomes, in his classical paper "Ueber Zelltheilung" ; there 

 he was able to prove that in spermatogonia of Amphibia the chromo- 

 somes preserve their integrity through the rest stage. Boveri is the 

 chief amplifier of this theory, and has added many facts corroborative 

 of it (1887, 1888, 1890, 1892). Other observations in corroboration 

 of this theory are especially furnished by Van Beneden & Neyt (1887), 

 RüCKERT (1892, 1894, 1895), Bokn (1894) and Francotte (1898). The 

 observations of myself (1898), McClung (1899) and Paulmiee (1899), 

 moreover, show that in the spermatocytes of Insects that curious meta- 

 morphosed chromosome, called by me the chromatin nucleolus, preserves 

 its integrity throughout the rest stage of the spermatocytes. 



