Fig. [257].—Diagrammatic representation of the alimentary, secretory, nervous, and reproductive systems of a male Porocephalus teretiusculus, seen from the side. The nerves are represented by solid black lines. (From W. Baldwin Spencer.)
1, Head-gland; 2, testis; 3, hook-gland; 4, hind-gut; 5, mid-gut; 6, ejaculatory
duct; 7, vesicula seminalis; 8, vas deferens; 9, dilator-rod sac; 10, cirrus-bulb;
11, cirrus-sac; 12, fore-gut; 13, oral papillae.
There appears to be no trace of circulatory or respiratory organs, whilst the function usually exercised by the nephridia or Malpighian tubules or by coxal glands, of removing waste nitrogenous matter, seems, according to Spencer, to be transferred to the skin-glands.
The nervous system is aggregated into a large ventral ganglion which lies behind the oesophagus. It gives off a narrow band devoid of ganglion-cells, which encircles that tube. It also gives off eight nerves supplying various parts, and is continued backward as a ninth pair of prolongations which, running along the ventral surface, reach almost to the end of the body (Fig. [257]). The only sense-organs known are certain paired papillae on the head, which is the portion that most closely comes in contact with the tissues of the host.
Pentastomids are bisexual. The males are as a rule much less numerous and considerably smaller than the females, although the number of annuli may be greater.
The ovary consists of a single tube closed behind. This is supported by a median mesentery. Anteriorly the ovary passes into a right and left oviduct, which, traversing the large hook-gland, encircle the alimentary canal and the two posterior nerves (Fig. [258]). They then unite, and at their point of union they receive the ducts of the two spermathecae, usually found packed with spermatozoa. Having received the orifices of the spermatheca, the united oviducts are continued backward as the uterus, a highly-coiled tube in which the fertilised eggs are stored. These are very numerous; Leuckart estimated that a single female may contain half a million eggs. The uterus opens to the exterior in the mid-ventral line a short distance—in P. teretiusculus on the last ring but seven—in front of the terminal anus. In L. taenioides the eggs begin to be laid in the mucus of the nose some six months after the parasite has taken up its position.
Fig. [258].—Diagrammatic representation of the alimentary, secretory, nervous, and reproductive systems of a female Porocephalus teretiusculus, seen from the side. The nerves are represented by solid black lines. (From W. Baldwin Spencer.)
1, Head-gland; 2, oviduct; 3, hook-gland; 4, mid-gut; 5, ovary; 6, hind-gut; 7,
vagina; 8, uterus; 9, accessory gland; 10, spermatheca.
The testis is a single tube occupying in the male a position similar to that of the ovary in the female. Anteriorly it opens into two vesiculae seminales, which, like the oviducts, pierce the hook-glands and encircle the alimentary canal (Fig. [257]). Each vesicula passes into a vas deferens with a cuticular lining. Each vas deferens also receives the orifice of a muscular caecal ejaculatory duct, which, crowded with mature spermatozoa, stretches back through the body. Anteriorly the vas deferens passes into a cirrus-bulb, which is joined by a cirrus-sac on one side and a dilator-rod sac on the other, structures containing organs that assist in introducing the spermatozoa into the female. The two tubes then unite, and having received a dorsally-placed accessory gland, open to the exterior by a median aperture placed ventrally a little way behind the mouth.
Life-history.—The egg undergoes a large portion of its development within the body of the mother. In Linguatula taenioides, which lives in the nasal cavities of the dog, the eggs pass away with the nasal excretions. If these, scattered about in the grass, etc., be eaten by a rabbit, the egg-shell is dissolved in the stomach of the second host and a small larva is set free. In Porocephalus proboscideus and others, which inhabit the lungs of snakes, the eggs pass along the alimentary canal and leave the body with the faeces. They also must be eaten by a second host if development is to proceed.
