( clxvi ) 



am quite satisfied that they are of very real value and assist- 

 ance not onh^ from the phylogenic but also from the taxouomic 

 point of view. 



If we now consider the sedoeagus, it will be necessary to 

 speak with extreme caution. So far as the Lepidoptera and 

 the Trichoptera. are concerned I believe it to be as valuable 

 a character as the external organs, but here I must explain 

 that I refer in this statement to that part of it defined by 

 Rothschild and Jordan as the penis sheath, i. e. the outside 

 hard chitinous case. I am fairly sure that the ductus ejacula- 

 torius with its tip which Pierce has named the " vesica " are 

 by no means satisfactory or safe characters on which to rely. 

 I do not mean that in some genera the}^ may not be useful, 

 but I have found quite frequently that whilst one species 

 of a genus may have considerable armature in the vesica 

 and also in the ductus ejacidatorius, another species in the 

 same genus may have none or next to none, and this would to 

 some extent agi-ee with the view of my friend, G. A. K. Mar- 

 shall, who tells me that he knows of Coleoptera in which the 

 sedoeagus is of the very simplest possible form, and that it 

 would be almost impossible to dift'erentiate one genus from 

 another in some such cases. I take it, however, that such 

 cases would occur only where the organ is extremely simple, 

 and it would follow almost for a certainty that directly pro- 

 gressive development began then differentiation would begin 

 also, and this we see in Sharp and Muir's valuable treatise, 

 the senior author of which tells me that he is still finding 

 marvellous and diverse developments in the vesica of the 

 order in question, and moreover that he considers this depart- 

 ment of entomology is destined to become of the first import- 

 ance ; an opinion that I most thoroughly concm- in. Perhaps 

 it may be thought that whilst I have been able to show difi'erent 

 degi'ees of development in the insects themselves, yet I have 

 not gone very far in argument, and up to a point this is true, 

 but the facts of the case lie in the figures presented before 

 you, and to a large extent may I not say that they speak 

 for themselves ? Nevertheless it appears to me to be correct 

 — or at least most probably correct — ^to say that, originally, 

 the anus and the aedceagus had each its own armature, pro- 



