CHROMOSOMES IN COREID HEMIPTERA. 99 



\ l< iwever, the embryo arising from this union would have been a 

 female, for all the products of the first cleavage nucleus would 

 contain two i<li< (chromosomes as in the oogonia. A chromosome 

 uroup taken from a female embryo is shown in Fig. 12, c. Even 

 these meagre results make it probable that the chromosomes 

 coming "in <>f the male and female pronuclei at copulation are 

 of the -a n it- n umber and show the same relative size differences as 

 tho-e which previously entered into the formation of the gametic 

 nuclei. 



1 ). The Cleavage and Blastoderm Nuclei. 



'l"h- < le.i\at;e nuclei are formed by successive division of the 

 t'i-i -iili/ati.n nucleus. After each division the daughter nuclei 

 move apart , each surrounded by a star-shaped cytoplasmic island. 

 The\ \\aml. -r toward the periphery, continually dividing by mito- 

 -.!-, and ih. -re form the blastoderm. Xo instances of amitosis 

 \\en- ..I.-. -r\t -d in these stages such as Wheeler ('89) described in 

 /?/<///<;. Ah hough but few first cleavage divisions were found, 

 the ( In OIMOM >mes in them do not differ from those of somewhat 

 later -ta^es described beyond. The cleavage mitoses all sho\\- 

 >pindle-, ( < ntrosomes and asters with diagrammatic clearness 

 and the chromosomes, though somewhat elongated, can be 

 c'.imii-d as readily as in the oogonial or spermatogonial divisions. 

 In metaphase each chromosome appearson the spindle split length- 

 \\ i-e and in anaphase the halves separate as in ordinary homotypic 

 division. In telophase the chromosomes at either pole become 

 \e~icular. fuse together and form a daughter nucleus. At first 

 tin- t ontt -in- of the resting nucleus entirely lacks staining power, 

 n<> mi. l.-oli of any kind appearing. As the time for the subse- 

 quent di\i-ion approaches, small Hakes of chromatin appear 

 \\ hi. h increase in number and gradually unite to form thechromo- 

 somes. In the cleavage stages, no definite chromatin nucleoli 

 or pla-moNonies could be seen with the methods of fixation em- 

 l)lo\i-d, nor was there any elimination of chromatin during the 

 earlier mitoses as described by Boveri in Ascaris. 



i. Archimems alter natus. 



A careful Minly of the eggs after fertilization revealed the fact 

 thai there are two sorts of embryos, one having 15 chromosomes 



