134 JOURNAL OF THE [Ociober, 



the ovipositor proper and the guiding sheaths: by J. L. Za- 



BRISKIE. 



Referring to his exhibits, Mr. Zabriskie said that the ovipositor 

 proper of Thalessa corresponds with that of Cryptus and all its 

 near relatives (see Mr. Riederer's drawings, this Journal, 

 vol. vi., Plate 25), being composed of three main pieces firmly in- 

 terlocked, but sliding upon each other throughout their entire 

 length. The dorsal piece is the largest. It is solid at the back, 

 nearly cleft in twain from beneath, allowing elastic expansion as 

 of a spring hinge, and having a " tongue " at the middle of either 

 side of the base. The two ventral pieces are counterparts of 

 each other, each being provided with a groove for interlocking 

 with and sliding upon the respective tongues of the ventral piece. 



The best published account extant of the oviposition by 

 Thalessa is that by Dr. Charles V. Riley in Insect Life, i., 172. 

 He shows that the operation is somewhat as follows: The insect 

 stands high upon its feet. The abdomen is raised in the air at 

 right angles with the thorax. The ovipositor, five inches long, 

 more or less, is managed by some of the feet, and its point is 

 brought to bear upon the wood of the tree. The halves of the 

 sheath do not enter the wood with the ovipositor proper, but are 

 used as props and stays for the boring tool during the operation. 

 By a movement from side to side and by bearing upon the ovi- 

 positor, the insect gradually forces back the base of the ovipositor 

 proper through the tip of the abdomen into a membrane which 

 issues between the sixth and seventh joints dorsally. There is 

 a wonderful muscular power in the anal joints, and the ovi- 

 positor is forced back until it forms a perfect coil, so that, when 

 the abdomen is stretched in a straight line to its utmost, the ovi- 

 positor within the membrane makes a circle almost as large as a 

 quarter of a dollar, the anal joint having made a three-fourths 

 turn within the membrane. During this operation the halves of 

 the sheath, which have not followed the ovipositor within|the 

 membrane, have been obliged to make a more or less irregular coil 

 opposite to and in front of the membrane on the ventral side. 

 As the ovipositor enters the wood the abdomen descends, the 

 distended membrane gradually subsides, and the halves of the 

 sheath make larger and larger loops above the abdomen. In 

 withdrawing the ovipositor the reverse action takes place, and 



