NOTES ON THE ANATOMY OF SCORPIONS. 123 
(m. ad.), the fibres of which run across from one opercular 
plate to the other, and which acts as an adductor muscle. 
Other muscles are present which serve to elevate and depress 
respectively the halves of the operculum. The genital aperture 
is single and median, but smaller than that of the female. 
The fact that the genital operculum in the male consists of 
two lateral pieces possesses a special interest in view of the in- 
terpretation which Lankester has recently put upon the relation 
and homology of these structures. 
Lankester states that,| “the history of development in 
Limulus shows that this genital operculum starts as two 
independent processes of the body, which are to be regarded 
as the appendages of the seventh segment. The operculum 
retains, throughout life, evidence of its double origin, and 
clearly resembles in form the five succeeding pairs of ap- 
pendages which carry the respiratory lamelle. In Scorpio, 
on the other hand, the genital operculum is relatively of very 
small size. Very little trace of having been formed by the 
union of two lateral appendages is exhibited by the genital 
operculum of Scorpio. At the same time its bifid margin 
speaks of such an origin .’ He further shows from 
the development of these parts, that the genital operculum 
arises as a pair of rudimentary appendages. 
My observations show that while in the female the median 
groove and its bifid margin really indicate a union of two 
lateral pieces into one single plate, in the male it remains 
throughout life as a pair of movable plates. These observations 
serve to corroborate Lankester’s views, and go far to establish 
the fact that the genital operculum of Scorpio represents a 
pair of appendages of the seventh somite as the pectines 
represent those of the eighth somite. 
I am indebted to Professor Bourne for the drawings of these 
structures. 
! «Limulus an Arachnid,” ‘Quart. Journ. Mier. Sci.,’ vol. xxi, 188], 
p. 524. 
