ZOOLOGY — MARK, NAPLES ZOOLOGICAL STATION, WILSON , 229 



Those of the second spindle are smaller, more irregular in shape, but often 

 resemble tetrads to such a degree that were it not possible to make a direct 

 comparison with the chromosomes of the first spindle, they might be mis- 

 taken for tetrads. This is because each element of a dyad has sometimes the 

 form of a dumb-bell. 



(7) The first polar cell disappears. While it is not possible, as yet, to 

 say whether it may not sometimes make its way, actively or passively, through 

 the zona pellucida, the only direct evidence at present indicates that it 

 degenerates while lying between the egg and the zona. We have a series of 

 stages showing a process of degeneration which begins with the disintegra- 

 tion of the chromosomes and ends, before complete disappearance, with a 

 very much flattened, clear, homogeneous body. 



Some of the points still to be worked out are : 



( 1 ) The precise method of the division of the tetrads, for which there are 

 few specimens. 



(2) The precise method of the division of the dyads, for which there are 

 no specimens. 



(3) The origin of the tetrads. 



(4) The origin and fate of the centrosomes and other polar corpuscles. 



Naples Zoological Station, Naples, Italy. Grant No. 419. For main- 

 tenance of tzuo tables. (For previous reports see Year Book No. 2, 

 p. cliv ; Year Book No. 3, p. 145 ; Year Book No. 4, p. 288, and Year 

 Book No. 5, p. 247.) $1,000. 



As in previous years, the grant was made to aid the laboratory in paying 

 for the maintenance of two research-tables. The director of the laboratory 

 assigned the tables during the past year to Mr. Addison Gulick, of Harvard 

 University; Dr. E. L. Rice, of Ohio Wesleyan University, and Mr. Edwin 

 C. Starks, of Stanford University. 



Wilson, Edmund B., Columbia University, New York, N. Y. Grant No. 

 370. Researches on the chromosomes of insects and other animals zvith 

 reference to the cytological basis of sex-production and Mendelian inher- 

 itance. (For previous report see Year Book No. 5, p. 250.) $500. 

 During the past winter great progress has been made with the series of 

 researches on which Dr. Wilson has been engaged. Nearly a thousand 

 microscopical preparations have been made, and over 300 photomicrographs 

 and 100 lantern-slides have been prepared. It is his intention to publish a 

 series of these photographs in the future. A few of the more important 

 results have been published in an article in the Biological Bulletin for 

 April, 1907, others have been announced in two papers read before the 

 American Society of Zoologists and the New York Academy of Sciences, and 



