ISOl.] 47 



On the CYNIPIDiE of the North Americau Oaks aud their Galls. 

 BY BAHON 11. OST£N SACKEN. 



The study of the galls or deformations produced by insects on different 

 plants, is one of the most interesting subjects in entomology and this 

 interest belongs especially to the numerous and varied galls produced by 

 the Ci/ni))i(hv, principally on the oak. Still, the difficulties attending the 

 study of the habits of the Ci/mpidse are so great, the peculiarity and, I 

 may say, the intricacy of these habits is so extraordinary, that the most 

 important questions concerning them remain as yet unsolved. This is so 

 true that it is not yet positively known, for instance, whether a consider- 

 able portion of the species of Ct/nipidse have any males or not, or what 

 their mode of reproduction is. 



The chief reason of the difficulty of this study is the close and pei'sistent 

 observation of natui'e it requires. Here, it is not sufficient to collect at 

 random, in order to work out at leisure the materials thus obtained ; here 

 one has to watch the growth of the gall on the tree for weeks and months; 

 in order to be enabled to make certain observations, one is bound to a cer- 

 tain season of the year and a certain locality and if the season is missed or 

 the locality cannot be reached at the requisite time, one has to wait a year 

 before the observations can be renewed. Few entomologists are so favor- 

 ably situated as to pui'sue a study of this kind for a sufficiently long period 

 of time and with such success, as to give the results thus obtained a shape 

 of relative completeness and the knowledge of the galls of Cynipidx would 

 make but little progress, if the gradual accumulation of single and scat- 

 tered observations of different observers did not supply in some measure 

 the place of a persistent and systematic study. Such scattered observa- 

 tions are therefore of the greatest value and entomologists cannot be too 

 much encouraged to publish them, or to communicate them to others for 

 publication. The value of such single observations depends chiefly on 

 their accuracy ; that is, the observer must see well and render onh/ 

 what he Jias !<een ; a condition much more difficult to comply with, in 

 matters of natural history especially, than is usually imagined. 



The aim of the present article is to publish certain observations which 

 the author may not be in a position to continue. At the same time, a 

 synopsis of the previous observations on the North American oak-galls 

 is given. 



One of the difficulties which obstruct the study of the Ci/nipi(hv is the 

 imperfection of their classification. Notwithstauding the great difference 

 in their habits, the variety in the structural characters seems to be very 

 limited. Up to the present time the chief stress has been laid on char- 



