1912] Morphology and Biology of Insect Galls 359 



The two observers, who deal with the development of galls from 

 eggs deposited on the outside of the host, hold entirely different opinions 

 concerning the early stages. Beyerinck^^ supposes that after the egg is 

 placed at the selected spot, the tissues under it grow very little, if at all, 

 but those immediately adjacent undergo rapid proliferation until the 

 egg is completely enclosed, forming a gall of the "Umwallung" type. 

 According to his view the larva possesses the power to stimulate the 

 tissues through the egg membrane without rupturing it. 



Weidel, on the other hand, holds an entirely different opinion con- 

 cerning the enclosing of the larva by the tissues of the host. He has been 

 able to convincingly demonstrate that in the gall Neuroterus vesicator 

 Schlecht, the cuticle of the leaf is punctured before the larva is completely 

 free from the egg membrane. "Die in der Eihaut noch vollstandig 

 eingeschlossene Larve durchbricht diese an einer Stelle und senkt in die 

 Epidermis des Blattes ein Organ ein durch das die Cuticula durchbrochen 

 und das pflanzliche Gewebe verletzt wird." — Weidel. ^^ The influence of 

 the larva^^ soon produces proliferation in the tissues of the leaf, and 

 following this a degeneration commences at the epidermis and extending 

 quickly forms a cavity of sufhcient size to hold the larva. Into the larval 

 chamber thus prepared the producer gradually passes, and the opening 

 through which it entered is soon closed by the growth of the stimulated 

 tissues. 



While the excellent work of Weidel cannot be questioned concerning 

 this particular gall, it is not necessary to assume that this is the only 

 method by which a larval cavity is formed. In my opinion the method as 

 described by Beyerinck is found in some of our American species of Andri- 

 cus and Dryophanta, reference to which will be made later. Weidel's 

 objections contained in the following quotation do not seem serious 

 enough to warrant the setting aside entirely of the "Umwallung" type 

 of development. "Gerade diese Stelle war es, die mich zu meinen Unter- 

 suchungen anregte, denn eine grosse Anzahl von Fragen bleibt bei diesen 

 Ausfiihrungen Beyerinck's unaufgeklart : Wie kommt es, dass an der 

 Stelle, wo das von der Larve abgesonderte Enzym am starksten wirken 

 muss, keine Vergrosserung der Zellen stattfinden soil, sondern nur in 

 einiger Entfernung? Was wird aus Epidermis unmittelbar unter dem 

 Ei? Aus Beyerinck's Figuren muss man annehmen, dass sie in Nahrge- 

 webe umgewandelt wird, da sie die Larve unmittelbar beriihrt. Wie 

 kommt das, "Sinken," oder, "Vergraben," zustande, Vorgange, fur die 

 ihn seine Erklarungen selbst nicht befriedigen?" — Weidel.'^* 



Concerning the first question, as to why the proliferation is more 

 pronounced around the larva than in immediate contact with it, it may 

 be stated that this is a usual occurrence in the lower groups of galls in 



