1914. j 129 



writers who have followed him. G-anglbauer's work on this family is 

 much below the level of most of the other parts of his very valuable 

 work, and a similar remark applies to Regimbart's study of the genus 

 Gyrinus. In fact, the subject has advanced but little in the last 50 

 years. I hope in this paper to carry it a little farther, but only a little, 

 and unless more rapid progress be made it will be some generations 

 before a satisfactory knowledge of the British Gyrinidse is attained. 

 I hope, however, by following Mr. Edwards' lead, and making athorough 

 study of the genitalia, we shall get a real advance, and it is with that 

 idea this paper has been drawn up and illustrated. 



The aedeagus is, however, only very imperfectly understood. The 

 lateral lobes when present in Coleoptera usually exhibit marked dis- 

 tinctions between the species. But in Gyrin us, though they are very 

 large, they yet are almost identical in all our British species. More- 

 over, the styli of the female resemble them in form, and are highly 

 peculiar. This leads me to suggest that their phallic function is sub- 

 ordinate to some bodily (or as Muir and I have termed it chrootic) 

 purpose. This, however, is one of the many points that will have to be 

 settled later on. 



Another distinctive character of the Gyrinid aedeagus, but one that 

 is probably of much less importance, is the relation of the lateral lobes 

 to the basal plate and to the median lobe. The lateral and median 

 lobes are very intimately connected, while the basal plate is only 

 attached to the lateral lobes by means of a very large connecting mem- 

 brane that allows the large basal plate to slide over and encase both 

 the median and the lateral lobes. Hence the tegmen (= basal plate 

 + lateral lobes) is peculiar. 



These facts, taken with the extreme adaptation of the chrootic 

 structures, emphasise the great isolation of the family Gyrinidze in the 

 Order Coleoptera. 



There appears to be no differentiated sac in Gyrinus, and I cannot 

 say what extension of duct there may be to accomplish fertilisation. 

 In Bytiscus, Hans Blunck (Zeitscbr. wiss. Zool. cii, 

 1912) has shown in a very valuable memoir that the 

 process of fecundation is accomplished by means of 

 a curious spermatophore formed during the copula. 

 So far as I know no information exists as to the 

 copula of Gyrinus. But I have a remarkable speci- 

 men of G. urinator that is about 60 years old, and 

 that exhibits a short portion of duct extended with 

 a peculiar body attached to it. I have thought it 



