ELTSHA MITCHELL SCIENTIFIC SOCIETY. 101 



exposed. This results from the larva locating very near the 

 surface so that its distended vesicular body breaks the surface 

 and becomes exposed. This does not seem to be a character of 

 very much value since many of the female cysts of Hetcrodera 

 radicicola are exposed. 



The chief morphological differentiating characters which have 

 been em[)loyed are as follows: The })osterior part of the body 

 of the female is rounded in Heterodera radicicola. In Hetero- 

 dera ScJiachtii'^ the posterior part of the body of the female 

 projects into a short, stout process in which is the vulva. 

 According to Strubell (loc. cit.) the exsertile spear is somewhat 

 differently constructed in the females of the two species. I 

 have only found one female which possessed the stout process 

 at the posterior part of the body. One of the most prominent 

 differentiating characters used in the case of the males is the 

 presence of the slender tail f)rocess in the cyst in Heterodera, 

 radicicola and its absence in Heterodera Schachtii. Dr. E. L. 

 Mark, of the Museum of Comparative Zoology, Cambridge, 

 Massachusetts, who, before my copy of Strubell arrived, kindly 

 compared for me some copies of my drawings with those of 

 Heterodera Schachtii by Strubell, and aided me in the interpre- 

 tation of some of the phases of egg segmentation, has made the 

 suggestion that possibly the slender tail })rocess in Heterodera 

 radicicola may be the result of the retention of the first larval 

 skiu which is lost in Heterodera Schachtii. After this sugges- 

 tion it has occurred to me that the first larval skiu (at second 

 moult) in those I have observed is cast at the time the larva 

 comes to rest preparatory to passing into the cystic stage. In 

 such moults I have only observed the skin as it was loosened 

 from the anterior part of the body. Strubell says, in the case 

 of Heterodera Schachtii (loc. cit., p. 44), that frequently the old 

 larval skin remains attached to the hinder part of the larval 

 envelope (''cyst") so that it has the appearance of being pointed. 



*Strabell, Untersuehungen uber den Bau und die Entvviekelung des Rubennemato- 

 den, Heterodera Schachtii, Schmidt. Bibliotheca Zoologica, Heft II, 1888. 



Muller, C. Mittheihmgen uber unseren Kultiirptianzen .'schadliche, das Geschleeht 

 Heterodera biidenden Warmer. Landwirthschaftiiche Jahrbucher. Ed. XIII, Heft I, 

 1884. 



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