OF THE GERM CELLS OF METAZOA. 



205 



Thus in Acholla there are eight in the spermatogonia which form four bivalent ones in 

 the spermatocytes ; in Sima and Mifym there are three bivalent ones in the spermato- 

 cytes, and accordingly probably six in the spermatogonia ; in Priomdm there are appar- 

 ently live in the spermatogonia, two of which unite in the spermatocytes to make one 

 bivalent one while the three others remain univalent. In (hloeoris there are in the 

 spermatocytes two bivalent and one univalent ; in Pwcilocapsm Unealus, one bivalent and 

 one apparently univalent; in P. gonitphorm certainly four, and possibly live, bivalent 

 chromatin nucleoli in the spermatocytes. In these forms one or more of the chromatin 

 nucleoli may have their component parts more or less widely separated, but these sepa- 

 rated components generally come together before the first maturation mitosis. 



Bivalent chromatin nucleoli which have their components inclose mutual apposition 

 appear always to be transversely divided in the first maturation division (reduction divi- 

 sion); for the behavior of those which arc; univalent I refer to the chapter on "Observa- 

 tions." 



Oncopeltus affords the interesting case where the two chromatin nucleoli of the 

 spermatogonia, are apparently each bivalent — bivalent elements in a, generation where all 

 the chromatin elements arc; usually supposed to be univalent. 



(c) The Peculiar Chromosome of Prolenor. 

 In Protenor — for the details compare the description in the chapter on " Observa- 

 tions" — there arc two chromatin nucleoli in the spermatogonia, which in the spermatocytes 

 unite to form a bivalent one, as we have just seen to be quite generally the rule in /femiptera. 

 But the largest of t.l i e chromosomes of the spermatogone mitoses, the " chromosome x," 

 does not behave in the growth period of the spermotocytes like the other chromosomes, 

 but is similar to a chromatin nucleolus in preserving a, compact form and in retaining the 

 saffranine stain. This is the odd chromosome, the eleventh, which does not combine with 

 any other during the synapsis stage, and which cannot be distinguished in the rest stage 

 of the spermatogonia because there it behaves exactly like the other chromosomes, and 

 takes part in the formation of the nuclear reticulum. This is the only case in the 

 Hemiptera where one chromosome becomes differentiated into a chromatin nucleolus for 

 the first time in the spermatocyte generation, unless the minute chromatin nucleoli of 

 Peribalus, Ccenus, Trichopepla and Gori&om may be found to have a similar history. 



(d) Function. 



All the observations show that the chromatin nucleoli are modified chromosomes, 

 which behave essentially like the chromosomes in mitosis but quite differently in the rest 

 stage. 



Paulmier (1899) has suggested that they are degenerate chromosomes. This would 



