30 [February, 



absolutely distinct from the body parts. They are not r^ somite, neither 

 can they be a sternal portion of a somite, because they form a continuous 

 tube. The basal part of the genital tube, to those who desire to consider 

 it a modified part of the true body, can only be of the natui-e of an 

 appendage or a modified pair of appendages. 



In the Helophoi'us encasement, the orientation cannot be reversed, 

 as it can in the case of the aedeagus. The tergum is much shorter 

 than the sternum, the latter being a little the longer in front and con- 

 siderably the longer behind. The dark chitinisations consist of a 

 median large, longitudinally somewhat pyriform area, and a transverse 

 basal area ; this latter is reduced in length in front, where it is joined 

 by the pyriform area, but extends backwards on each side of the latter 

 for a considerable distance. The dark chitinisations of the sternal plate 

 are a median longitudinal one extending the whole length ; the sides of 

 it part or diverge in front in a V-like fashion ; the arms of the top of 

 the V are quite horizontal in each direction and each arm connects with 

 a slender longitudinal very hard band. This latter hard band connects 

 behind with the extremity of the external anterior part of the curved 

 base of the tergum, and by this means a very beautiful arrangement of 

 the nature of a spring is produced. The concentration of the 

 chitinisations to form this spring is highly remarkable, and is well dis- 

 played in specimens that have been submitted to the action of caustic 

 potash to an extent sufficient to make the parts transparent, but not 

 to destroy any of the outline. 



The whole of the structures at the apex of the abdomen, with the 

 aedeagus form a very simple but perfect mechanical arrangement. The 

 anal orifice is occluded by the falling of the posterior part of the pyri- 

 form area of the tergum of the encasement, but is freed, when 

 necessai-y, by the action of the springs of the encasement. In a similar 

 manner, when the genital tube is extended, no matter can pass through 

 it until the pyriform area is lifted, and until the lips of the median 

 orifice are opened. This latter is pretty certainly effected by the agency 

 of the struts and the pressure of the lateral lobes on these. 



I hope that later on we may be able to give some illustrations that 

 will render my account of the aedeagus more easily comprehensible. 



(To he continued.) 



