223 



On Some Peculiarities in the Reproductive System of 



certain of the acarina. 



By A. D. Michael, F.L.S., F.R.M.S. 



{Read April 25th, 1879.) 



Plate XIIJ. 



I have to-night allowed myself to be tempted to occupy a little of 

 your time with matter, the greater part of which is not new. I 

 have, however, thought that the subject is sufficiently curious and 

 interesting to form my excuse, particularly as it is little known in 

 this country, and therefore may probably be fresh to many. 



When I commenced studying the Acarina I found myself in 

 a difficulty in regard to the reproductive organs. These, from their 

 importance, would naturally be a somewhat primary consideration, 

 and the great variety of position and organization in various fami- 

 lies, and the differences of opinion between authors regarding them, 

 call for special remark from any one studying that portion of the 

 Arachnida. One difficulty which is manifest to the beginner is how 

 the act of coition is accomplished at all. In some families, as the 

 Oribatidce, Cheyleti, &'c, the sexual organs are placed in the abdo- 

 men, but, in the great majority of cases, the opening is placed on 

 the ventral surface of the cephalothorax and the abdomen being 

 usually large and unjointed it is not apparent how the often very 

 short male organ is brought in contact with the vulva of the female. 

 Apterologists have made various suggestions to explain this diffi- 

 culty, based, it is to feared, more upon their own ideas of proba- 

 bility, than upon actual observation, while an analogy to the spiders 

 was naturally looked for. It is to the admirable observations of M. C. 

 Robin that we -owe what is probably the true solution of what might 

 have continued to be a difficulty, had it not been for certain features 

 of that division of the Sarcoptidce, which we usually call Dennaleichi, 

 and which Messrs. Robin and Megnin call " Sarcoptides plumicoles" 

 a class of Acari entirely parasitic upon birds, but, in the opinion of 



