No. 46041] -| STUDIES ON PLANT CELL— VII. 579 
dividing once, so that every germ cell receives a single hetero- 
chromosome of whatever sort. Fertilization then brings the 
heterochromosomes together again in pairs until the next period 
of chromosome reduction. This history is then parallel to 
Sutton's account of the lubber grasshopper (Brachystola), the 
difference being that the latter form presents a remarkably 
graded set of paired chromosomes. Montgomery regards the 
small chromosomes and the accessory chromosome as structures 
tending to disappear in a process of evolution from a higher 
chromosomal number to a lower. 
Moenkhaus (:04) crossed reciprocally two species of fishes 
(Fundulus heteroclitus and Menidia notata) and obtained hybrid 
embryos which reached an advanced stage of development. 
The chromosomes of the parents are readily distinguished by 
size and form. These chromosomes were followed throughout 
` the development of the hybrid embryo and were found to retain 
their peculiarities so that the two sets may be easily separated 
in favorable tissues. This investigation furnishes some of the 
strongest evidence of the individuality of the chromosome and 
the complete independence throughout the life history of the 
two sets derived from each parent. Could these hybrid embryos 
be raised to maturity we should expect to find during spermato- 
genesis and oógenesis an association of the chromosomes in 
pairs, those of paternal extraction with those of maternal to 
form the bivalent chromosomes preliminary to the reducing divi- 
sions, and a distribution to the sexual cells in varying propor- 
tions which would, however, give a very large ratio of relatively 
pure germ cells. ne 
Baumgartner (:04) in studies upon spermatogenesis in the 
cricket (Gryllus) was able to distinguish the chromosomes. by 
their form, following them through the mitoses of reduction. 
Most of the chromosomes have the form of straight or bent rods 
but there are apparently two rings in each set in G. domesticus. 
The variation in the form of chromosomes in the nucleus is well 
known but it has not been supposed that a definite form might 
be characteristic of an element and be maintained throughout 
the successive mitoses of a life history as seems probable from 
Baumgartner's results. 
