182 



Mr. K. J. Marks : A colony of Stentor jyolymorphus, colourless 

 variety, showing a common mucilaginous basis built up through 

 excretion. 



Mr. J. Rheinberg : Exhibit illustrating Complementary Inter- 

 ference Colours. Actinocyclus Ralfsii, shown by means of a 

 double-image disc (see ante, p. 151) of clear glass, which is placed 

 over the objective. A dioptric and a diffraction image are 

 formed of the same object side by side. Where the colours due 

 to interference are formed in the dioptric image, the comple- 

 mentary coloui-s will be formed in the diffraction image. 



/ 

 May 3rd, 1901. 



Mr. A. E. Hilton : Nematohelminthes (Thread-worms), showing 

 the genital and anal pores. 



Mr. T. N. Cox (jun.) : Leaf of Anacharis alsinastrum, a North 

 American plant, now naturalised in this country, showing circu- 

 lation of sap, especially near the midrib. 



Mr. W. R. Traviss : The "Blood Rain" Plant. Found in a tank 

 at Camden Town. 



Mr. H. Morland : Two slides of lobes of proboscides of Blow- 

 Ely, Calliphora erythrocephala, and Yellow Dung- Fly, Scatophaga 

 stercoraria, prepared to show the so-called "teeth." Presented 

 to the cabinet by Mr. W. H. Harris, Cardiff. 



The " teeth " arise from modifications of the basal plates of the 

 pseudo-tracheae. In the Blow- Fly they consist of three distinct 

 superimposed rows, the thin free ends being slightly in advance 

 of the immediately preceding row. The primary, or superficial, 

 row consists of eleven to twelve strap-shaped organs, the margins 

 of which are recurved for a considerable portion of their length, 

 giving the appearance of a split tube, with the fracture slightly 

 opened. The intermediary row consists of fewer " teeth " than 

 the primary set, and is built up on a different plan, the base of 

 each "tooth" arising from two distinct points on the right and 

 left of the two adjacent pseudo- tracheae, and becoming fused 

 together towards the free end. All the " teeth " are clef t into a 

 V-shaped form at their extremities. In the case of the Dung-Fly 



