THE BEHAVIOR OF THE CENTROSOMES IN THE 

 FERTILIZED EGG OF MYZOSTOMA GLABRUM, 

 LEUCKART. 



WILLIAM MORTON WHEELER. 



The material of Myzostoma glabrum on which the following 

 observations were made was collected at Naples during Feb- 

 ruary and March of the current year. The work on the fecun- 

 dation of the Qgg was brought to a conclusion in the laboratory 

 of the Institut Zoologique at Liege, and I gladly seize this 

 opportunity of thanking the director of the Institut, Professor 

 Ed. Van Beneden, both for his constant and friendly guidance 

 during my studies, and for the many favors and privileges 

 which he so cordially bestowed upon me. A fuller account of 

 my observations, with a discussion of the pertinent literature, 

 will be published later. 



The minute eggs of Myzostoma glabrum were fertilized arti- 

 ficially and killed in Flemming's fluid (weaker formula). The 

 sections (5/* thick) were stained on the slide with Heidenhain's 

 iron-alum haematoxylin, followed by a saturated aqueous solu- 

 tion of "Orange G." 



The large germinal vesicle occupies the middle of the ellip- 

 tical unfertilized ^gg (Fig. i), and contains, besides the huge 

 vacuolated nucleolus, 12 small chromosomes, each consisting 

 of two short rods swollen at their ends. The lower portion of 

 the Qgg is a mass of granular plasma ; the remaining portions 

 are found to be considerably vacuolated in sections, and to 

 contain more or less yolk. 



The head of the spermatozoon (Fig. i) has a peculiar struc- 

 ture which has been overlooked by other investigators of the 

 Myzostomida. In the living condition it presents alternating 

 bands of different refraction, but when stained the more refrac- 

 tive bands form a series of chromatic discs embedded in an 

 achromatic substance. Where the head tapers at either end 

 the discs become smaller and more difficult to resolve. I have 



