270 



SCIENCE 



[N. S. Vol. XXXVII. No. 946 



Caswell Grave (Johns Hopkins University) : The 



Egg of Oplimra, its Yolk Content and Course of 



Development. 

 Or. T. Haegitt (Northwestern University) : The 



Oogenesis of Campanularian Hydroids. 



The egg cells of Campanularia flexuosa arise 

 from the basal half of an ordinary epithelial cell 

 of the entoderm, the distal half remaining an 

 epithelial cell; or else they arise by the trans- 

 formation of an entire entoderm cell in the pedicel 

 of the gonophore. In either case the cell so pro- 

 duced is transformed directly into an egg cell 

 without any divisions occurring. Since the ento- 

 dermal epithelial cells from which the egg cells 

 arise are not different from the neighboring cells 

 which retain their epithelial function, and since 

 the distal half of a divided cell remains in posi- 

 tion lining the coslenteric cavity and retains its 

 function (the proximal half forming an egg cell), 

 there is clearly no continuity of the germ-plasm, 

 the egg arising from a so-called somatic cell. 



Coincident with the marked and rapid growth 

 of the egg the nucleolus (which is partly chro- 

 matin) breaks up into many fragments of various 

 sizes and shapes, and becomes highly vacuolated. 

 At the same time there appear small granules in 

 the cytoplasm against the membrane of the ger- 

 minal vesicle, and also similar small granules are 

 present inside the membrane; these are found to 

 be nucleolar fragments, some of which are chro- 

 matic in character. In addition to these indica- 

 tions of the escape of chromatin from the ger- 

 minal vesicle there are currents in the cytoplasm 

 extending away from the nucleus, as shown by the 

 arrangements of the cytoplasmic granules. These 

 currents cease when the nucleolus has entirely dis- 

 appeared from the nucleus through fragmentation 

 and dissolution, and this period is also the end of 

 the growth period of the egg. The nucleolar 

 material which has left the nucleus goes to form 

 the yolk spherules of the egg. 



During the growth of the egg the nuclear 

 reticulum has remained unchanged by the modi- 

 fications and transformations of the nucleolar sub- 

 stance which has been dissolved and cast into the 

 cytoplasm. When the nucleolus is practically all 

 gone and the growth of the egg has ceased the 

 chromatin of the reticulum produces the chromo- 

 somes of the polar spindle, which are ten in 

 number. In spite of the extensive chromatin 

 emission, coming from the dissolving nucleolus, 

 the chromatin remaining in the nuclear reticulum 

 is still more than is necessary for the formation 

 of the chromosomes, and the greater part of it 



escapes into the cytoplasm in the form of granules 

 when the germinal vesicle breaks. That which is 

 not thus scattered forms the chromosomes. 



To account for the large amount of chromatin 

 which escapes from the nucleus there must be a 

 formation of chromatin within the nucleus during 

 the growth period of the egg, and the nucleolus 

 is conceived to be the place where the chromatin 

 is produced and transformed for the different 

 functions it has to perform. In this origin of new 

 chromatin, and in the extreme dissipation of 

 chromatin during and after growth, it is believed 

 that we have strong evidence against the con- 

 tinuity of chromatic material, and hence of the 

 chromosomes. The chromatin is a metabolic prod- 

 uct changing and transforming as all other con- 

 stituents of the living cell. 



J. F. Abbott (Washington University) : The 

 Blood Cells and their Respiratory Pigment in 

 ThMla-sema. 

 H. E. Jordan (University of Virginia) : A Com- 

 parative Study of Mammalian Spermatogenesis 

 tvith Special Reference to the Heterochromo- 

 somes. 



Among the forms examined, including mon- 

 goose, cat, squirrel, pig, rabbit, white mouse, 

 sheep, horse, mule, bull and dog, heterochromo- 

 somes are lacking in the male germ-cells of the 

 first five, and present in the remainder. The 

 available evidence favors more the interpretation 

 in terms of a bipartite or compound X-element 

 than of an associated X and T group (idiochro- 

 mosomes ) . 



In view of the fact that heterochromosomes 

 have recently been reported in man and rat 

 (Guyer), armadillo ^Neuman and Patterson), 

 guinea-pig (Stevens) and opossum and bat (Jor- 

 dan), the evidence indicating similar elements in 

 the above enumerated group of six common mam- 

 mals would seem to warrant the conclusion that 

 sex-chromosomes are very generally present in 

 mammals. Universality of presence seems vitiated 

 for the present by the fact that in another group 

 of five mammals such elements seem unquestion- 

 ably lacking. It might be assumed that such 

 elements are actually present in the male germ- 

 cells, but so small or labile as to elude detection 

 by present methods, or not presenting the usual 

 morphology of heterochromosomes during the pro- 

 phase stages. The unmistakable presence, how- 

 ever, of a " split-accessory ' ' in the female germ- 

 cells (primary oocyte) of the cat, as recorded 

 by Winiwarter and Sainmont, and the absence of 



