3:2 THE ANATOMY OF IXVERTEBRATED ANIMALS. 



always consists of a single median tergal sclerite, to the in- 

 ferior angles of which are connected two small more or less 

 triangular pieces, each of which carries a long st^'liform ap- 

 pendage. There is a single median sclerite, which is the most 

 important part of the boring apparatus ; two small sclerites 

 are united with the lateral angles of this piece, and there are 

 two other elongated sclerites which constitute a valvular 

 sheath. Thus, according to Lacaze-Duthiers's view, in the 

 sting of JBomhus (Fig. 94) h is one of the elongated lateral 

 sternal sclerites, which with its fellow forms a slieath for the 

 rest of the apparatus ; f is the median sternal sclerite ; it is 

 pointed and grooved on its sternal surface ; while e, one of 

 the lances, is a process of the tergal half of the somite. Each 

 lance is sharp and slender, and its tergal edge fits upon the 

 margin of the groove of the median style, in such a manner 

 as to be able to slide backward and forward upon it. The 

 sternal edges of the two lances meet in the middle line, and, 

 together with the median sternal piece, inclose a canal which 

 serves to convey the secretion of the poison-gland into tlje 

 wound made by the sting. In the operation of stinging, the 

 median piece serves as a sort of " director " for the two lances. 

 However, recent investigations into the development of 

 stings and ovipositors,' e. g., the sting of the Hive-bee, and 

 of the Wasp and the ovipositor of an Ichneumon-fly [Cri/ptifS 

 migrator), show that while the median grooved piece and the 

 two sheath-pieces arise from papillae developed upon the 

 sternal surface of the ninth abdominal somite of the larva, 

 the lances are the result of the metamorphosis of papillae 

 seated on the sternal surface of the eighth somite ; and these 

 papilL^ are so similar to those from which the limbs are de- 

 veloped, that it becomes (to say the least) probable that they 

 represent true appendages of the somites to which they are 

 attached, rather than mere modifications of the sclerites of 

 the body-wall, as Lacaze-Duthiers supposed them to be. In 

 like manner, the examination of the development of the ovi- 

 positor of Jyocustcf. viridissima has proved that, of the three 

 pieces of which each half of it is composed, two are developed 

 from the sternum of the ninth and one from that of the eighth 

 somite. But the two median pieces of the ninth somite do 



» Kraepelin, " Untersiicliunoren iiber den Ban, Mechanismus iind EntTvicke- 

 lunsssreschiphte des Stachels der bienenarticren Thiere " iZeitf^ehrift fiir wiss. 

 Zoohgie, 1S73^ ; and T)ewitz. " Ceber Ban und Entwiekelunsr des Stachels und 

 der Leerescheide " {ZfiUchrift fxtr wiss. Zooloaie, 1875). See ali^o the observa- 

 tions of Packard, " On the Development and Position of the Hymenoptera," 

 1866. 



