Anatomy of the Male Genital Tube in Coleoptera. 601 



branch proceeds to each testis. In a pecuHar structure of 

 this kind it is evident that the homologisation of the parts 

 is attended Avith some special difficulties. Extensibility 

 and retractibility of the tube are carried to an extraordin- 

 ary perfection, and the length of the tube is in some cases 

 enormous compared with the size of the creature, and yet 

 the " orifice " may in one position of the organ be placed 

 near the distal, in another position near the proximal 

 extremity. The same " orifice " is in fact at one moment 

 of the creature's existence placed inside and quite near to 

 the centre of the body, while at another moment it may 

 be placed far away, at the extremity of the extended tube. 

 The walls of this protean structure become in some places 

 hard, and form sclerites. The study of these sclerites is 

 one of the chief aids in our endeavour to understand the 

 changes the tube may have undergone during its evolution. 



The homologies of the various parts of the male genital 

 tube are, within certain limits, very easy to follow, and 

 even in some of the most extreme forms can be made out 

 by anatomical comparison. But beyond the limits we 

 have alluded to, the questions become very difficult, and 

 will really only be settled by studies of the ontogeny that 

 at present are not forthcoming. As misconception has 

 been, and still is prevalent to a considerable extent, there 

 are a few general points to which we must allude. Accord- 

 ing to our view the genital tube commences Avhere the 

 body wall ends. Anatomically it is not easy to decide 

 where that spot is, because body wall and genital tube 

 are continuous. 



Embryologists consider with good reason that the 

 stomodaeum and proctodaeum are the poles of the body 

 wall, therefore all parts that have their origin on the 

 dorsal aspect of these openings are tergal, and all parts 

 on the ventral aspect are sternal. The genital tube, being 

 ventral of the anus, can therefore contain no tergal parts ; 

 though one or more sternites may enter into its composition. 



Hopkins * considers our tegmen in Pissodes as " repre- 

 senting the apodeme of the ninth tergite." Bugnion f 

 considers that in Cissitcs testaccus the median lobe (" gout- 

 tiere interne ") is derived from the ninth segment, and the 

 tegmen (" gouttiere externe ") from the tenth segment. 



* U. S. Dept. Agr. Technical Series, No. 20, Part I, 1911. 

 t Bull. Soc. Ent. d'Egypte, 4""' Fascicule, 1910. 



