OF EPPING FOREST. 27 



It is narrowed toward the apex at which is situated the 

 papilla ig). 



The posterior plate (e) is also narrowed towards the apex and 

 broad at the base. 



The sheath (h) is made up of two pieces which together 

 form a groove in which the two spiculae, or boring apparatus 

 proper, can move. 



These spiculae (/) are attached to the triangular plate and 

 are usually toothed at the apex. 



The five muscles which are attached to the plates act on 

 the posterior plate by contraction and expansion, giving the 

 spiculae a backward and forward movement. 



The egg itself consists ol a round egg body (Fig. 4, at) 

 which eventually contains the embryo, and a long stalk-like 

 process (k) which is useful in two ways. During the process of 

 oviposition the egg body is not sent down inside the ovipositor, 

 but the egg-stalk is clasped and carried down by the two 

 spiculae, the main portion of the egg remaining outside, as the 

 groove inside the sheath is not large enough to admit it. 



In the case of such galls as Biorhiza terminalis, when the egg 

 is laid in the bud, a passage is first formed by the insect down to 

 the cambium layer. The egg, when it reaches the extremity of 

 the ovipositor, is not detached from the spiculae, but the egg 

 body is placed at the mouth of the groove formed in the bud 

 from which the ovipositor is partially withdrawn and pushed 

 down until it reaches the cambium layer. The ovipositor is 

 furnished with a number of tactile hairs whereby the insect is 

 kept informed, as it were, of tiie progress of the egg to its proper 

 destination. 



Besides acting as a means of attachment to the spiculae 

 by which the latter can seize the egg, the egg tube is also 

 used as a respiratory organ whereby oxygen can be admitted to 

 the embryo developing in the interior of the embedded egg body, 

 For this purpose it is left lying in the canal formed by the 

 insect previously to the deposition of the egg. One insect may 

 lay from six hundred to seven hundred eggs, and oviposition 

 may extend over a period of three or four days. As before 

 mentioned the egg must be laii in the cambium layer, which 

 envelopes the whole of the plant and represents the growing- 

 zone. Fggs laid in winter buds are particularly liable to failure, 



