OP THE GERM CELLS OF METAZOA. 



197 



always thirteen chromatin elements. Two of these are much smaller than the others 

 (M 2), and are obviously the univalent chromatin nucleoli, which at this stage do not 

 make up a bivalent one. The eleven large elements are chromosomes, and since all of 

 them appear dumbbell-shaped on lateral view, they are all bivalent. Two of the eleven 



<;l "'° ^mea have a markedly greater volume than t]w, others (/ 2, Fig. 238), and 



these correspond to the four large chromosomes of the spermatogonia (7, Figs. 230, 237); 

 that is to say, in the synapsis the four large chromosomes derived from Uie spermatogo- 

 nia, unite together to form two bivalent ones, and , a large one never appears to unite 

 with a small one. 



The first maturation mitosis is a, reduction division, and each daughter cell (second 

 •spermatocyte) receives eleven whole univalent chromosomes. 



III. en ee a i, Conclusions. 



/. The process of spermatogenesis in the Hemiptera, and Ihc individuality of the 

 chromosomes. 



In the Hemiptera heteroptera we find, as generally elsewhere in the Metazoa, a 

 number of generations of spermatogonia in each of which all the chromatin elements 

 are halved in metakinesis (apparently in all cases equationally), the last generation pro- 

 ducing spermatocytes of the first order. These spermatocytes enter upon a, growth 

 period of long duration, which is followed by the first maturation division, resulting 

 I" the formation of spermatocytes of the second order; and in the second maturation 

 division the spermatocytes of the second order are divided into spermatids. There are 

 always exactly two maturation divisions and no more. The metamorphosis of the 

 spermatids into the spermatozoa, has not been studied by me, and has not the broad com- 

 parative interest of the preceding stages, hut it has been described by Henking (1890) 

 and Paulmier (1899). 



The growth period of the spermatocytes is of the greatest interest, for here are a 

 remarkable series of changes not found in any other generation of the germ cells nor, so 

 far as is known, in any somatic cells. And the most important of these changes are 

 found in the synapsis stage of the growth period. The synapsis stage is well-marked in 

 all the Hemiptera examined by me without exception, characterized by a dense grouping 

 of the chromatin loops; the citations given by me in my study on Peripatus (1901) 

 show that it seems to be present, in almost all, if not all the Metazoa in which the 

 spermatogenesis and ovogenesis has been carefully examined. The dense grouping of 

 the chromosomes in this stage is not an artifact produced by faulty fixation methods, as 

 McClung (1900) has recently maintained, tor exactly the same appearances are to be 



