Vol. IX. July, 1905. No. 2 



BIOLOGICAL BULLETIN 



THE FORMATION OF THE FIRST POLAR SPINDLE 

 IN THE EGG OF BUFO LENTIGINOSUS. 



I 



HELEN DEAN KING. 



In a previous paper on " The Maturation and Fertilization of 

 the Egg of Bitfo lentiginosns" (King, 10), the formation of the 

 first polar spindle and the subsequent divisions of the chromo- 

 somes were very incompletely described owing to a lack of ma- 

 terial showing the details of these processes. During the spring 

 of 1899, a large number of toads were collected soon after they 

 had emerged from their hibernation, and from three of them suf- 

 ficient material was obtained to give a more complete history of 

 the late maturation processes. A short account of my study of 

 this period in the development of the egg has already appeared 

 (i i) ; a detailed account is given in the present paper. 



I. MATERIAL AND METHODS. 



As soon as possible after the toads were captured they were 

 killed by pithing and the body opened at once to ascertain the 

 condition of the ovaries. In a great majority of cases the eggs 

 were found free in the ccelomic cavity and were, therefore, of no 

 use for the purpose intended, as previous investigations had 

 shown that eggs which have broken through the wall of the 

 ovary invariably contain a fully formed maturation spindle lying; 

 at the periphery near the center of the black hemisphere. 



In several instances, all of the eggs were still attached to the 

 walls of the ovaries when the toad was killed. In these cases 

 some of the eggs were put at once into a dish of fresh spring 

 water and the rest were left in the body of the female which was 



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