286 TRANS. ST. LOUIS ACAD. SCIENCE. 



what smaller egg of the gall-inhabiting mother ; 3rd, the ? egg 

 from the winged mother, rather more ellipsoidal, and 0.40 mm. 

 long when mature ; 4th, the c? egg from same, } less in length and 

 rather stouter ; 5th, the impregnated egg, just described, 0.32 mm. 

 long and still more ellipsoidal. We have also the singular spec- 

 tacle of an egg from the winged mother increasing from 0.34 mm. 

 (its size when laid) to 0.40 mm. (its size just before hatching) ; 

 giving birth to a perfect insect 0.40 mm. long, and this in turn, 

 without any nourishment, laying an egg 0.32 mm. long. A being 

 is thus born, and, without food whatsoever, lays an egg very near- 

 ly as large as that from which she came. 



From the observations here recorded I would draw the follow- 

 ing conclusions : 



1. We can no longer entertain the hope of any practical good 

 from the knowledge of the nidus chosen by the winged mothers, 

 as the destruction either of these or of their eggs — scattered as 

 they are on the leaves all through a vineyard — is out of the ques- 

 tion. The objects are too small to be practically searched for, 

 and it is virtually impossible to prevent the spread of the disease 

 in this stage. We might almost as well try to prevent mildew 

 by the destruction of the invisible floating spores that must at 

 times pervade the atmosphere of a vineyard. The hope enter- 

 tained by Lichtenstein that the winged mothers would congre- 

 gate and be attracted to some particular plant must, I think, be 

 abandoned. 



2. The only preference shown in this respect would seem to be 

 for those leaves that are most downy or tomentose ; and from this 

 view of the case we get another probable reason why the varie- 

 ties of Labrusca which are characterized by an abundant downi- 

 ness on the under surface of the leaves suffer most from the insect. 



3. Having already had the young from the impregnated egg of 

 Rileyi hatch in about a fortnight after it was laid — having shown 

 in previous writings that this species winters in the larva state, and 

 not in the impregnated egg as does the European querciis ; and, 

 remembering, further, that vastatrix resembles Rileyi in winter- 

 ing as larva, it is safe to conclude that the impregnated egg of vas- 

 tatrix will also hatch the same season that it is laid, and that we 

 cannot apply to it the term "winter egg" which Balbiani applies 

 to the impregnated egg of quercus. It is not unlikely that, since 



