Bibliography.
(383) O. Bütschli. “Entwicklungsgeschichte d. Cucullanus elegans.” Zeit. f. wiss. Zool., B. XXVI. 1876.
(384) T. S. Cobbold. Entozoa. Groombridge and Son, 1864.
(385) T. S. Cobbold. Parasites: A Treatise on the Entozoa of Man and Animals. Churchill, 1879.
(386) O. Galeb. “Organisation et développement des Oxyuridés,” &c. Archives de Zool. expér. et génér., Vol. VII. 1878.
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Acanthocephala.
The Acanthocephala appear to be always viviparous. At the time of impregnation the ovum is a naked cell, and undergoes in this condition the earlier phases of segmentation.
The segmentation is unequal (Leuckart, No. [393]), but whether there is an epibolic gastrula has not clearly been made out.
Before segmentation is completed there are formed round the ovum thick protecting membranes, which are usually three in number, the middle one being the strongest. After segmentation the central cells of the ovum fuse together to give rise to a granular mass, while the peripheral cells at a slightly later period form a more transparent syncytium. At the anterior end of the embryo there appears a superficial cuticle bearing in front a ring of hooks.
The embryo is now carried out with the excreta from the intestine of the vertebrate host in which its parent lives. It is then swallowed by some invertebrate host[159].
Another very remarkable human parasite belonging to the same group as Dracunculus is the form known as Filaria sanguinis hominis, or Filaria Bancrofti[158].
In the intestine of the invertebrate host the larva is freed from its membranes, and is found to have a somewhat elongated conical form, terminating anteriorly in an obliquely placed disc, turned slightly towards the ventral surface and armed with hooks. Between this disc and the granular mass, already described as formed from the central cells of the embryo, is a rather conspicuous solid body. Leuckart supposes that this body may represent a rudimentary functionless pharynx, while the granular mass in his opinion is an equally rudimentary and functionless intestine. The body wall is formed of a semifluid internal layer surrounding the rudimentary intestine, if such it be, and of a firmer outer wall immediately within the cuticle.
The adult Echinorhyncus is formed by a remarkable process of development within the body of the larva, and the skin is the only part of the larva which is carried over to the adult.