1890.] NEW-YORK MICROSCOPICAL SOCIETY. 101 



arrangement, they are prevented from separating laterally. As 

 the two dorsal parts are fastened together in one piece only 

 along a fine line on the surface, this allows the two parts to be 

 separated from each other for a certain distance, like the two 

 sides of a hinge. Yet as soon as any force ceases to separate 

 them, the elasticity of the joint will bring together again the 

 two sides of the ovipositor. The passage of the egg from the 

 oviduct into the slit, formed by the two sides of the ovipositor, 

 tends to separate these parts, and at the same time, by the elas- 

 ticity of these latter, the egg is firmly held in the slit. By the 

 reciprocal movement of the sliding parts the egg is forced 

 forwards. Yet the pressure exercised on the egg by this means 

 is alleviated by the flexibility and thinness of the sides of the 

 ventral parts forming the slit. Besides this the tube of the 

 ventral parts is filled by a soft plastic substance, in which is em- 

 bedded a trachea of good size, all acting like an air-cushion. 

 Two small projections at the edges of the ventral parts prevent 

 the egg from escaping sidewise. When not in use, these " ap- 

 pendices " are kept between the two ventral parts, close to their 

 inner sides, by the elasticity of the connecting joints. 



The pupa shows five wide tubes, bent around the end of the 

 abdomen, and reaching well forward on the dorsal part of the 

 insect. In these five tubes are contained, separate from each 

 other, the one dorsal part, the two ventral parts, and the two 

 sheaths. The less the development of the pupa has progressed, 

 the less is visible of the finer structure of the single parts. The 

 parts representing the tubes of the future ovipositor proper are 

 homogeneous, showing no, or, later on, but slight differentiation. 

 In the dorsal part no slit is visible, and but a trace of the pro- 

 jecting tongues, and the grooves in the ventral parts do not yet 

 appear. Thus the union of the one dorsal and the two Ventral 

 parts of the pupa, into the ovipositor of the imago, takes place 

 at the time when the mature insect bursts open the pupal skin, 

 and forces its way out. Then the soft tongues enter the grooves, 

 and the parts assume their proper shape and hardness. In this 

 manner, it seems to me, takes place the formation of the ovi- 

 positor, a complex organ, composed of the formerly separated 

 single parts. 



