3i6 Transactions of the Canadian Institute [vol. ix 



is much more active in providing for its own welfare than in the higher 

 types and the plant renders a relatively smaller amount of assistance. 

 As the stimulation of the animal participant becomes more effective, the 

 plant is coerced into providing more suitable conditions for the maturing 

 of the producer, which consequently becomes less active on its own be- 

 half and more dependent on the host. 



While glands are invariably larger in the gall tissues than in the 

 corresponding normal stems, Stagmatophora ceanothiella Cosens fur- 

 nishes the only example where there is a distinct increase in the number 

 of glands. 



An unusual cell division occurs in the species 5. ceanothiella Cosens 

 and G. gallcBasterella Kellicott. The daughter cells are in clusters, 

 usually four in number, clearly showing they have originated from a com- 

 mon progenitor. The septations between the cells are always very 

 straight and the elongated nuclei are pressed closely against the division 

 walls. This form of mitosis produces only a very small portion of the 

 gall tissues in these species, but in the Dipterous gall Neolasioptera per- 

 foliata Felt (Fig. 23) it originates nearly the whole mass. This form will 

 be referred to again and the cell division illustrated in the part of this 

 paper dealing with Dipterous galls. 



As I have repeatedly found the opening through which the larva 

 of Eucosma scudderiana Clemens has entered the stem, it is certain that 

 this Lepidopterous producer always oviposits on the outside of the host, 

 and this may prove to be true of the entire group. 



Order Diptera. 



The anatomy of the following species is considered : — 

 Order Diptera, 



Fam. Cecidomyidae. 



Cecidomyia bulla Walsh. 

 Cecidomyia balsamicola Lintner. 

 Cecidomyia impatientis O.S. 

 Cecidomyia majalis O.S. 

 Cecidomyia ocellaris O.S. 

 Cecidomyia pellex O.S. 

 Cecidomyia triticoides Walsh. 

 Lasioptera corni Felt. 

 Lasioptera impatientifolia Felt. 

 Neolasioptera perfoliata Felt. 

 Rhabdophaga batatas Walsh. 

 Rhabdophaga strobiloides Walsh. 



