Fig. 4.—The small Egyptian fluke (Distoma heterophyes), viewed from behind. The large ventral sucker, supplementary disk, uterus, testes, simple divided intestine, vitellarium, and pulsatile vesicle are conspicuous. Original.
Distoma heterophyes, Von Siebold.—This minute parasite, measuring only 3/4 of a line in length, was discovered by Dr Bilharz, of Cairo, in the intestines of a lad, post-mortem, in the year 1851. A second similar instance occurred, when several hundred examples were collected and afterwards distributed amongst the helminthologists of Europe. Through the kindness of Leuckart two of the worms eventually reached myself. From one of these the accompanying figure was drawn. For the purpose of supplying a full diagnosis I have elsewhere described this worm as presenting an oblong, pyriform outline, attenuated in front, and obtusely rounded behind; body compressed throughout, the surface being armed with numerous minute spines, which are particularly conspicuous (under the microscope) towards the head; oral and ventral suckers largely developed, the latter being near the centre of the body, and about twice the diameter of the former; pharyngeal bulb distinct and separate from the oral sucker, and continued into a long œsophagus, which divides immediately above the ventral acetabulum; intestinal tubes simple, gradually widening below and terminating near the posterior end of the body; reproductive orifices inconspicuous, but evidently placed below and a little to the right of the ventral sucker, at which point they are surrounded by a special accessory organ, resembling a supernumerary sucker; uterine folds numerous and communicating with small but conspicuously developed vitelligene glands; testes spherical and placed on the same level in the lower part of the body; ovary distinct; aquiferous system terminating inferiorly in a large oval contractile vesicle, the latter opening externally by a central foramen caudale.
Apart from its minuteness, moreover, this trematode is especially characterised by the possession of a very remarkable apparatus surrounding the reproductive orifices. It consists of an irregularly circular disk, measuring 1/125″ in diameter, and having a thick-lipped margin, which supports seventy fish- basket-like horny ribs comparable to the claw-formations seen in the genus Octobothrium. According to Bilharz these ribs give off five little branches from their sides, but Leuckart could not see them in his specimens. Leuckart estimated the length of these horny filaments to be 1/1250″, whilst their breadth was 1/3570″. On the whole we may regard this organ as a complicated form of “holdfast” designed to facilitate or give efficiency to the sexual act. I may here also state that this structure is by no means unique; for, if I mistake not, it exists in an equally developed degree in the young trematode which Dr Leared found infesting the heart of a turtle. Leared believed that he had found an ordinary distome; an opinion to which I could not give my assent, seeing that the organ described by him as a “folded, ventral sucker” presented a very different aspect to the oral sucker displayed by the same animal. Without doubt, however, the organ in his so-called Distoma constrictum is analogous to the supplementary “holdfast” existing in Distoma heterophyes. The views which I originally advanced as to the source and condition of the parasite are probably correct.
As regards the structure of Distoma heterophyes, I have only to add that a special set of glandular organs is situated on either side of the elongated œsophagus, but the connection between these organs and the digestive apparatus has not been clearly made out. Leuckart compares them to the so-called salivary glands found in Distoma lanceolatum, and says, “The presence of such a glandular apparatus is also indicated by the more ventral position of the oral sucker, and the development of the cephalic margin.” The conspicuous contractile vesicle terminating the excretory system is developed to an unusually large extent, exhibiting in its interior multitudes of the well-known active molecular particles. Lastly, I have only to add that the eggs of Distoma heterophyes measure 1/990″ in length by 1/666″ transversely.
Fig. 5.—The eye fluke (Distoma ophthalmobium). Showing the suckers and intestinal tubes. After Von Ammon.
Bibliography (No. 8).—Bilharz, “Beitrag zur Helminth. humana,” ‘Zeitsch. für wissenschaftl. Zool.,’ s. 62, 1851.—Cobbold, ‘Entozoa,’ p. 195, 1864.—Küchenmeister, F., ‘Parasiten,’ 1855, s. 210, Eng. edit., p. 276, 1857.—Leared, “Description of Distoma constrictum,” ‘Quarterly Journal of Micros. Science,’ new series, vol. ii, 1862.—Leuckart, R., l. c., s. 613, 1863.—Moquin-Tandon, on the Genus Fasciola, l. c., 1861.—Weinland, on Dicrocœlium, l. c., p. 86, 1858.
Distoma ophthalmobium, Diesing.—There is every reason to believe that the small flukes found by Gescheid and Von Ammon in the human eye were sexually immature worms, but since it cannot be decided as to what adult species they are referable I prefer to notice them under the usual title. Possibly these eye-worms may be referred to D. lanceolatum, as suggested by Leuckart. However that may be, I deem it unnecessary to repeat the details recorded in the treatises quoted below. The largest examples measured only half a line or about one millimètre in length.
Bibliography (No. 9).—Cobbold, ‘Entozoa,’ p. 191.—Gescheid (D. oculi humani), in Von Ammon’s ‘Zeitsch. f. Ophth.,’ iii, and also in Ammon’s ‘Klin. Darstell. d. Krankheit d. Menschl. Auges.,’ vols. i and iii.—Küchenmeister, Eng. edit., p. 287.—Leuckart, l. c., s. 610.—Nordmann (Monostoma lentis), “Mikr. Beitr.,” Heft. ii, ‘Vorwort,’ s. ix, 1832.