As the best observers agree in stating that the Acephalocyst is impassive under the appli cation of stimuli of any kind, and manifests no contractile power either partial or general, save such as evidently results from elasticity, in short, neither feels nor moves, it cannot, as the animal kingdom is at present characterized, be referred to that division of organic nature.
It would then be a question how far its chemical composition forbids us to rank the Acephalocyst among vegetables. In this king dom it would obviously take place next those simple and minute vesicles, which, in the aggregate, constitute the green matter of Priestly, (Protococcus viridis, Agardh;) or those equally simple but differently coloured Psychodiariir, which give rise to the red snow of the Arctic regions, ( Protococcus Ker mesianus.) These " first-born of Flora" con sist in fact of a simple transparent cyst, and propagate their kind by gemmules developed from the external surface of the parent.
Or shall we, from the accidental circum stance of the Acephalocyst being developed in the interior of animal bodies, regard it, as Rudolphi would persuade, in the same light as an ulcer, or pustule,—as a mere morbid pro duct ? The reasons assigned by the learned Pro .
mutes being ed from the internal surface of the cyst, where they grow, and, in like man ner, propagate their kind, so that the successive genera tions produce the appearance descri bed by Hunter and other pathologists.
The membrane fessor' do induce us to consider the Acephalo cyst as a being far inferior in the scale of orga nization to the Cysticercus; but still not the less as an independent organized species, sharing its place of development and sphere of existence in common with the rest of the Entozoa.
Acephuloeystis endogena. Pill-box Hydatid of Hunter, (fig. 56). This species is so called from the =cum Fig. 56. stance of the gem beingof the cyst is thin, delicate, transparent, or with a certain pearly semi-opacity ; it tears readily and equally in every direction, and can, in large specimens, be separated into laminae. The phenomenon of endosmose is readily seen by placing the recent Acepha locyst in a coloured liquid, little streams of which are gradually transmitted and mingle with the fluid of the parasite. The vesicles or gemmules, developed in the parietes of the cyst, may be observed of different sizes, some of microscopic dimensions, others of a line in diameter before they are cast off, see fig. 56,
where a shows the laminated membrane, b the minute Acephalocysts developed between its layers.
The Acephalocyst of the Ox and other Ru minant Animals differs from that of the Hu man Subject in excluding the gemmule from the external surface, whence the species is termed Acephaloeystis exogena by Kuhl. Both kinds are contained in an adventitious cyst, com posed of the condensed cellular substance of the organ in which they are developed.
The Genus Echinococcus is admitted by Rudolphi into the Order Cystica, less on ac count of the external globular cyst, which, like the Acephalocyst, is unprovided with a head or mouth, than from the structure of the minute bodies which it contains, and which are described as possessing the armed and suctorious head characteristic of the Ceenuri and Cysticerci. It must be ob served that Rudolphit does not ascribe this complicated structure to the vermiculi of the human Echbwrocrus on his own authority, and speaks doubtfully respecting the coronet of hooklets and suctorious mouths of the ver miculi contained in the cyst of the Echinoroecus of the Sheep, I log, &c.
The Erlanococcus hominis, (fig. 57,) which occurs in cysts in the liver, spleen, omen turn, or mesentery, is composed ofan exter nal yellow coriace ous, sometimes crus taceous tunic, and an internal transparent, firm, gelatinous membrane. The form of the contained ver miculi is represented in the magnified view subjoined, (fig. 58,) taken from the Elnanto grafia humana of Delle Chiaje.
Miiller* has recently described a species of Echinococcus voided with the urine by a young man labouring under symptoms of renal disease. The tunic of the containing cyst was a thick white membrane, not naturally divided into the animalcules floating in the con tained fluid presented a circle of booklets and four obtuse processes round the head ; the pos terior end of the body obtuse : some of them were inclosed in small vesicles floating in the large one; others presented a filamentary pro cess at their obtuse end, probably a connecting pedicle which had been broken through.