DEVELOPMENT OE PEKIPATUS CAPENSIS. 
765 
iscera are supplied richly with tracheae. Their manner of distribution is shown in 
Plate LXXIII. fig. 2, a , which shows the arrangement on one of the secreting-tubes of 
the slime-gland. 
The vessels run in bundles of two, three, or sometimes as many as six together in 
an irregular zigzag course, crossing one another in all directions, so as to form a 
tangled irregular meshwork. They usually run separately for the last part of their 
course, and they terminate simply without enlargement, apparently with closed ends. 
The vessels are very fine, being only about ‘003 millim. in diameter, but are very con- 
spicuous when filled with air and viewed by transmitted light. When examined with 
very high powers they show transverse markings, which appear to indicate the existence 
of an imperfectly developed spiral fibre within them (Plate LXXIII. fig. 2, b). The 
fibre, or rather band, is broad in proportion to the diameter of the vessel ; it is appa- 
rently very imperfectly differentiated, and not tenacious enough to be partially uncoiled 
when a vessel is torn across, as is the case in the tracheae of insects. 
The distribution of the tracheae to the uterus and oviducts is seen in Plate LXXIV. 
fig. 1. The tracheae very rarely branch ; but branching does occur. Plate LXXIII. 
fig. 2 represents an instance of branching in the tracheae of the uterus. 
The spiracles, or openings of the tubes from which the tracheae take origin, lie in the 
depressions between the conical warty excrescences with which the skin is covered. 
They are small and difficult to see when the epidermis is spread out and examined with 
the microscope. They seem to be mere cracks between the superficial epidermic cells ; 
and no definite arrangement of these cells around them was observed, although most 
carefully sought for. The skin contracts when removed from the body and placed on 
a slide, and the spiracles close up and are most difficult to find. If a large specimen 
of Peripatus be killed by drowning, the animal dies in a state of extension, and the 
spiracles remain patent. A row of minute oval openings may then be seen with a 
lens extending along the median line of the ventral surface of the body. The openings 
are situate with tolerable regularity in the centres of the interspaces between the pairs 
of members, but additional ones occur at irregular intervals. Other similar openings 
occur in depressions on the inner sides of the conical foot protuberances. If the skin 
in which these openings occur be dissected off and spread out under the microscope no 
definite arrangement of cells around them is to be observed, and they collapse at once, 
having no chitinous ring or such structure. 
Generative Organs. — Peripatus was described as hermaphrodite by Grubb, that 
observer having mistaken the slime-glands of the animal for testes ; in reality the 
sexes are distinct. There appear to be no outward characteristics by which a male can 
be distinguished from a female. Out of about thirty specimens dissected two thirds 
were females. All the males but one were very small, not more than 2 centims. in 
length ; and it was at first concluded that the males were always smaller than the- 
females ; but one female was met with of only 2 centims. in length ; and the last 
specimen dissected, which was 5 centims. in length, turned out to be a male. The 
