262 PROCEEDINGS OF THE ACADEMY OF [March, 



Pole views of the monaster stage of the first maturation mitosis 

 (PI. X, fig. 1) show seven chromatin elements of relatively equal 

 volume, and lateral views of the chromosomes in this stage show 

 that they are all dumbbell-shaped, and hence probably bivaJent 

 (fig. 2). This mitosis results in a transverse (reduction) division of 

 all these elements. Very frequeutly one of them is seen to be 

 characterized in having its two components of very unequal 

 volume. 



Since these preparations were stained merely by the iron-htemo- 

 toxylin method, the presence of chromatin nucleoli could not be 

 positively determined owing to the lack of difi^t^rential staining. 

 But in the prophases of the first maturation mitosis can be seen a 

 large true nucleolus, and two smaller rounded bodies (generally of 

 different volumes) which are soiuetimes in mutual apposition, and 

 sometimes not. If the latter are chromatin nucleoli, they are much 

 smaller than any of the seven bivalent chromatin elements of the 

 maturation division, so that the latter are possibly all unmodified 

 chromosomes. 



This species of the Tingitidce, in having such a small number of 

 chromosomes, may be regarded rather as a specialized than a j^rimi- 

 tive form. 

 2. Corixa verticalis Fieber. 



The chromosomes could not be counted in the monaster stages of 

 the spermatogonia. Two testes were examined. 



Pole views of the monaster stage of the first maturation mitosis 

 (PI. X, fig. 3, in which two of the chromosomes are seen laterally) 

 show twelve chromatin elements, of which one regularly is placed 

 in the centre of a circle composed of the remaining eleven. Lateral 

 views (fig. 4, in which four of the large and two of the small 

 elements are shown) show that all these elements are dumbbell- 

 shaped, and hence probably bivalent. Three are much smaller 

 than the remaiiiing nine, and the very smallest is the one that 

 occupies the centre of the chromosomal plate. All these elements 

 divide by a transverse (reduction) division, and in the daughter 

 cells (second spermatocytes) the chromosomes are arranged all close 

 together in the equatorial plane ; it is the case in a number of 

 species of the Hemiptera that the chromosomes show different plan? 

 of arrangement in the two maturation mitoses. 



In the post-synapsis stage there is found in the nucleus a peri- 



