No. 464.] 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 o5genesis 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. 



Baumgartner (:o4) 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. 



