AND THE DEVELOPMENT OF THE MYRIAPODA. 
101 
nation, is thicker and more opake the nearer it lies to their outlet. In those in- 
dividuals which have not arrived at their full growth, many of the sacs are only par- 
tially developed. Some of them are narrow, elongated, and have not yet begun to 
secrete (7); and others are only beginning to make their appearance at the sides of 
the tubes (k). In all of them, the interior or mucous lining is distinctly seen to be 
continuous with that of the large efferential tubes, and in those which appear to be 
secreting, the base of each vesicle is constricted by the mucous lining within, which 
seems to form a valve (e). 
The general structure of the generative organs is very simple throughout the 
whole of the Iulidse, but many curious peculiarities occur in the larger species. 
Thus, in one of the African types, the double organ of intromission (fig. 3. a) is pre- 
hensile, each part having the form of a distinct claw, between the moveable joints of 
which passes out the elongated half-corneous penis. These parts are covered in 
anteriorly by a horny valve, somewhat of a triangular form, and the whole occupies 
an oval space on the under surface of the seventh segment, corresponding to that 
usually occupied by the legs. Anteriorly, the two large efferential ducts (b) termi- 
nate in the penis in very fine tubes, beyond which they become more and more 
dilated, but instead of being close together, they are placed at some distance from 
each other throughout their whole course, and lie, one on each side, above the 
nervous cord, but are connected by transverse ducts from near their very outlet in 
the penis to their lateral development into caeca (c). In this part of their course 
they would seem to perform the office, not only of efferential ducts, but also of re- 
ceptacles for the seminal fluid, with which both the transverse ducts ( d ), and certain 
short dilatations from their inner side, are greatly distended. In one species, lulus 
? I found fourteen of these transverse ducts, and in another, more than twenty. 
In other respects, these organs of reproduction, in the larger species, resemble those 
of lulus terrestris, being covered with an abundance of short caeca. In this part of 
their structure , they approach closely to some of the Annelida, in which, as in the 
common Leech, the caeca of the male organs are regarded as accessory vesiculae semi- 
nales. But the great number of these caeca in lulus, and the presumed absence of 
other structures which may be regarded as the proper testes of the animal, together 
with the greatly distended condition of the transverse ducts and efferential tubes 
towards their anterior part, have inclined me to the opinion now advanced respect- 
ing their true nature ; although from their analogy with the Annelida, and also from 
the circumstance of my not having yet been able to follow out the main ducts to their 
commencement, the subject must still be regarded as open to further inquiry. With 
regard to the product of secretion in these organs, I have never yet found anything 
but a granulous fluid in the cseca, apparently similar to the granules in the higher 
animals, from which spermatozoa are produced ; but this might have arisen from 
the immature recent specimens I was alone able to obtain. It would be interesting 
to ascertain whether these germs of spermatozoa are produced in the cseca, as there 
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