Page:EB1911 - Volume 01.djvu/141

 least there is also a genital ganglion. Some scattered papillae may possibly be sense-organs.

The Acanthocephala are dioecious. There is a “stay” called the “ligament” which runs from the hinder end of the proboscis sheath to the posterior end of the body. In this the two testes lie (fig. 3). Each opens in a vas deferens which bears three diverticula or vesiculae seminales, and three pairs of cement glands also are found which pour their secretions through a duct into the vasa deferentia. The latter unite and end in a penis which opens posteriorly.

The ovaries arise like the testes as rounded bodies in the ligament. From these masses of ova dehisce into the body cavity and float in its fluid. Here the eggs are fertilized and here they segment so that the young embryos are formed within their mother’s body. The embryos escape into the uterus through the “bell,” a funnel-like opening continuous with the uterus. Just at the junction of the “bell” and the uterus there is a second small opening situated dorsally. The “bell” swallows the matured embryos and passes them on into the uterus, and thus out of the body via the oviduct, which opens at one end into the uterus and at the other on to the exterior at the posterior end of the body. But should the “bell” swallow any of the ova, or even one of the younger embryos, these are passed back into the body cavity through the second and dorsal opening.

The embryo thus passes from the body of the female into the alimentary canal of the host and leaves this with the faeces. It is then, if lucky, eaten by some crustacean, or insect, more rarely by a fish. In the stomach it casts its membranes and becomes mobile, bores through the stomach walls and encysts usually in the body-cavity of its first and invertebrate host. By this time the embryo has all the organs of the adult perfected save only the reproductive; these develop only when the first host is swallowed by the second or final host, in which case the parasite attaches itself to the wall of the alimentary canal and becomes adult.

A curious feature shared by both larva and adult is the large size of many of the cells, e.g. the nerve cells and the bell.

O. Hamann has divided the group into three families, to which a fourth must be added.

(i.) Fam. Echinorhynchidae. This is by far the largest family and contains the commonest species; the larva of Echinorhynchus proteus lives in Gammarus pulex and in small fish, the adult is common in many fresh-water fish: E. polymorphus, larval host the crayfish, adult host the duck: E. angustatus occurs as a larva in Asellus aquaticus, as an adult in the perch, pike and barbel: E. moniliformis has for its larval host the larvae of the beetle Blaps mucronata, for its final host certain mice, if introduced into man it lives well: E. acus is common in whiting: E. porrigeus in the fin-whale, and E. strumosus in the seal. A species named E. hominis has been described from a boy.

(ii.) Fam. Gigantorhynchidae. A small family of large forms with a ringed and flattened body. Gigantorhynchus gigas lives normally in the pig, but is not uncommon in man in South Russia, its larval host is the grub of Melolontha vulgaris, Cetonis auratus, and in America probably of Lachnosterna arcuata: G. echinodiscus lives in the intestine of ant-eaters: G. spira in that of the king vulture, Sarcorhampus papa, and G. taeniodes in Dicholopus cristatus, a cariama.

(iii.) Fam. Neorhynchidae. Sexually mature whilst still in the larval stage. Neorhynchus clavaeceps in Cyprinus carpio has its larval form in the larva of Sialis lutaria and in the leech Nephelis octocula: N. agilis is found in Mugil auratus and M. cephalus.

(iv.) Apororhynchidae. With no proboscis. This family contains the single species Apororhynchus hemignathi, found near the anus of Hemignathus procerus, a Sandwich Island bird.

ACANTHUS (the Greek and Latin name for the plant, connected with , a sharp point), a genus of plants belonging to the natural order Acanthaceae. The species are natives of the southern parts of Europe and the warmer parts of Asia and Africa. The best-known is Acanthus mollis (brankursine, or bears’ breech), a common species throughout the Mediterranean region, having large, deeply cut, hairy, shining leaves. Another species, Acanthus spinosus, is so called from its spiny leaves. They are bold, handsome plants, with stately spikes, 2 to 3 ft. high, of flowers with spiny bracts. A. mollis, A. latifolius and A. longifolius are broad-leaved species; A. spinosus and A. spinosissimus have narrower, spiny toothed leaves. In decoration, the acanthus was first reproduced in metal, and subsequently carved in stone by the Greeks. It was afterwards, with various changes, adopted in all succeeding styles of architecture as a basis of ornamental decoration. There are two types, that found in the Acanthus spinosus, which was followed by the Greeks, and that in the Acanthus mollis, which seems to have been preferred by the Romans.

ACAPULCO, a city and port of the state of Guerrero on the Pacific coast of Mexico, 190 m. S.S.W. of the city of Mexico, Pop. (1900) 4932. It is located on a deep, semicircular bay,