Ixxili 
vent at the posterior, are obviously what would arise as soon as 
any specialization of function in the series of zooids occurred. It 
is not, therefore, surprising that we never find these change their 
position. But for the respiratory and generative organs there is 
no such necessity for fixity of position, and as they existed 
originally in every segment, we can well conceive how, as 
articulate forms become more and more modified, it would 
sometimes be useful to the compound animal for these organs 
to become abortive or developed in different parts of the 
body. We have seen that this is to some extent the case 
with the former organs, but it occurs to a much greater extent 
with the latter. 
The most generalized form is to be seen in the intestinal 
worms, each segment of which possesses a complete hermaphrodite 
reproductive apparatus ; so that, in this respect, no less than in 
their capacity for spontaneous fission, these creatures are really 
what we should expect the early type of compound animals to 
be. This, however, is a rare case, but even in the much higher 
leeches there are testes in no less than nine of the segments, and 
Dr. Williams discovered a direct passage from the spermatheca to 
the ovaries, which seems to indicate internal self-fertilization. 
It is, however, in the lower Arthropoda that we find the most 
curious diversities in the position of these organs. In the 
Glomeride the genital openings in both sexes are situated in the 
third segment, just behind the insertion of the second pair of 
limbs. In the Polydesmide the female organs are in the third 
segment, while those of the male are in the seventh segment. 
In Julus the same organs are situated in the fourth and seventh 
segments respectively. The Chilopoda, on the other hand, have 
them near the end of the body, as in most insects. In the 
Acarina the ovaries open on the middle of the abdomen or on the 
under side of the thorax, either between or behind the last pair of 
legs. In spiders the seminal orifice is at the base of the abdomen, 
but the palpi are the intromittent organs; these are spoon-shaped, 
and are besides armed with horny processes, hooks, and other 
appendages, and must be looked upon as true generative organs. 
In the Astacide the sexual organs of the male are at the base of 
the first pair of abdominal legs, those of the female at the base 
of the third pair. Among the true winged-insects there is one 
remarkable case of abnormal position of these organs, in the 
L 
