EUBYTOMTLiE. 9 



such violation of the great law of the unity of habits can be met with 

 anywhere in nature. 



" Certainly, if preceding authors had referred this species to its 

 proper genus (it was referred to Isosonia in 1843) I should not have 

 been so unwilling to believe in its being a true vegetable-feeder. As 

 soon as I became personally acquainted with it the mystery was solved 

 at once." 



The female of I. Hordei resembles the female of I. Vitis in 

 structure, but the male, as appears by the figure in the ' American 

 Entomologist,' vol. ii. p. 330, differs widely from that of I. Vitis, 

 and approaches much nearer to the typical species of Isosoma. 



The immense number of species in the Chalcidias, and the numerous 

 instances of very close mutual resemblance in their forms, afford large 

 materials for research and for debates whether the differences are of 

 specific character or mere variations, and one more extract from Dr. 

 Walsh's works will show his opinion with regard to the words species 

 and variety. In a notice of the forms of Eurytoma he says, 

 " Whether they be really varieties, or whether they be distinct species, 

 depends — according to my view — upon the difficult and almost 

 insoluble question," &c. He distinguishes Eurytoma and Isosoma 

 by some characters which are not mentioned by Foerster, who first 

 gave a detailed description of the differences between the two genera. 

 His distinctions apply clearly to the typical species of each genus, 

 such as E. plumata and I. verticillata, but there are other species in 

 which these distinctions can hardly be traced. The distinctions are 

 as follows : — 



Eurytoma. — Body partially contractile, with a deep finely sculp- 

 tured groove for the reception of the middle femora reaching from 

 the base of the middle coxa to a point immediately beneath the 

 insertion of the front wing. Antennas 8-jointed, 9-jointed in E. 

 gigantea. 



Decatoma. — Body contractile, as in Euiytoma, and with a similar 

 groove for the middle femora. Antennas of the male 7-jointed, 

 filiform, the club slightly compressed. Antennas, of the female 

 8-joiuted, gradually clavate, the club considerably compressed. 



Isosoma. — Bod}' not contractile and with no groove to receive the 

 middle femora. Antennas 9-jointed. 



Dr. Foerster distinguishes Decatoma from Eurytoma and from 

 Isosoma by the bristles on the hind tibias of the former genus, but 

 this character is insufficient to distinguish several of the species. 



Dr. Walsh continues his remarks on the Eurytomidas as 

 follows : — " It is a very general law in Chalcidias that each successive 

 pair of legs is more and more marked with black." " And so with 

 other families of insects ; each will be found to be marked according 



