190 THE ORIGIN OF VERTEBRATES 
and a lateral posterior, which covers the first pair of gills, or lung- 
books, as they are called. In this type (Fig. 77) the genital ducts 
terminate in a common chamber or uterus, the nature of which will 
be further considered. 
As has been pointed out by Blanchard, the terminal genital 
organs of the scorpions and the Pedipalpi vary considerably in the 
different genera, especially the male genital organs. The general 
type of structure is the same, and consists in both male and female 
of vasa deferentia, which come together to form a common chamber 
before the actual opening 
to the exterior. This com- 
mon chamber has been 
called in the female scor- 
pion the vagina, or in 
Thelyphonus the uterus, 
I shall use the latter term, 
in accordance with Tar- 
nani’s work, and the corre- 
sponding chamber in the 
male will be the uterus 
masculinus, 
A considerable discus- 
Fic. 77.-OPERCULUM AND FOoLLowIne SEG- sion has taken place about 
MENTS OF Mate THELYPHONvs. the method of action of the 
Opercular segment is marked out by thick black external genital organs in 
line. Ut. Masc., uterus masculinus; Int. Op., the members of the scorpion 
internal opening of uterusinto genital chamber; : : nt Ne 
Ext. Op., common external opening to genital tribe, into which it is hardly 
chamber (Gen. Ch.) and pulmonary chamber. necessary to enter here. 
: The evidence points to the 
conclusion that in all these forms the operculum covers a median 
single chamber or uterus, into which the genital ducts open on each 
side, the main channels of emission being provided with a massive 
chitinous internal framework. We may feel certain that in the old 
extinct sea-scorpions, Eurypterus, etc., a similar arrangement existed, 
and that therefore in them also the median portion of the operculum 
covered a median chamber or uterus composed of the amalgamation 
of the terminations of the two genital ducts, which were originally 
separate, as in Limulus. 
The observations of Schmidt, Zittel, and others show that the 
