Horse 38, 36 



Rabbit 42, 28-36, 22 



Cat 36 



Hog 20, 18 



Fowl 18, 17 



Rana catesbiana (Frog) 29 



Nematus ribesii (Currant saw fly) ... 8 

 Diabrotica vittata (striped cucumber 



bettle) 21 



Cricket {G. domesticus) ' 21 



Gypsy Moth 31 



Eristalis tenax 12 



Culex pipiens (common mosquito) ... 6 



Spittle insect (P. spumarius) 24 



Pyrrhocoris apierus 24 



Acridium granulatus 13 



Protenor beljragei 14, 13 



Lygaeus bicrucis 14 



Oncopeltus fasciatus 16 



Cicada 20, 19 - 



(c) — Maturation and Reduction 



1 1 isjcnown that t he nucleus_of the zygote or fertilize d 

 egg-cell contains twice"aFmany]^£hlQ rnosomes as either o Y 

 the ^anTe tes. THe chro mosonies of the gametes at ter ull- 

 zation do"Ti6rTirse;IguQem ain sepa ^^ clear, there - 



7oreptK^::t!iefCmusr6e"a]re ductioiTtn the niimber of chrx )- 

 r nosomes^p rior to the Tormat jon of the garnetes to one-hal f. 

 e l§e~~TpLe immber ihT]^I-zygate.I^uld double_,mlil^acl^ 

 generation, i his"'~re3uction has actuSlTy^een observea . 

 *" It is "now~generally agreed that the reduction in the 

 number of chromosomes in the higher animals occurs in the 

 last two-cell divisions by which the definite germ-cells arise ; 

 that is, when the ovarian oocyte gives rise to the mature 

 ovum and two or three polar bodies, and when a spermato- 

 cyte divides into four young spermatozoa. (See Fig. 6). 



In plants, the reducing division occurs at the forma- 

 tion of the spores, which arise in sets of fours. 



In the formation of sporangia of ferns, the central cell 

 gives rise to tapetmn and archesporial cell. The latter soon 

 forms sporogenous or grand-mother cells of the spores. 

 When the mother-cell divides to form four spores, the num- 

 ber of chromosomes is halved. This number remains con- 



(1) — The recent studies of Miss Carotliers of the chromosomes of 

 certain Orthoptera (1913 and 1917) point very definitely to the 

 conclusion that the assortment cf the chromosomes at maturation 

 is a random one, thereby bringing the chromosome theory into 

 harmony with the Mendelian law. 



133 



