Like all other animals, snakes are infested with a multitude of vegetable and animal parasites, both external and internal. About 300 species of Ophidian parasites have been recorded; yet our knowledge of them is very imperfect. Although some 2,000 species of snakes are known, parasites have not been recorded for more than 168 species, and in the great majority of these (102) only a single parasite: a tick, a hÆmogregarine, or some intestinal worm. Owing to the more frequent opportunity of dissecting them, the common menagerie snakes have yielded better records, notwithstanding the fact that they usually lose most of their parasites through constant handling, prolonged fasting, and artificial surroundings. Thus, we have a list of thirteen species for the Indian Python molurus, and one of twenty-two species for the Boa constrictor. But no systematic search appears to have been attempted, save, perhaps, in the case of a few European species.

It is interesting to notice that it was the finding of an Ophidian parasite which prompted Francesco Redi to write his famous “Observations on the Living Animals which are found within Living Animals.” This work, a veritable treatise of comparative parasitology, published in 1684, caused the great naturalist, physician, and poet to be regarded as the father of that science. He tells us that in dissecting a curious dicephalous Vipera aspis, caught at Pisa, he found within the intestines a number of roundworms (Ascaris cephaloptera), and on the surface of one of the two lobes of the liver five cysts enclosing a small worm, which he rightly ascribed to the same species.

The parasites of snakes are here enumerated by Dr. L. W. Sambon, in systematic order.

Arthropoda.—Two families of the class Arachnida, the IxodidÆ and the LinguatulidÆ, furnish numerous species parasitic on snakes.

Of the Ticks (IxodidÆ) we find, as a rule, species of the genera Amblyomma and Aponomma, the latter genus being almost entirely confined to Reptiles. A single species of the genus HÆmaphysalis (H. punctata, Can. and Franz, 1877) has been reported once from Vipera aspis. A few larval forms found on various snakes have been reported under the generic name Ixodes, but they probably belong either to Amblyomma or Aponomma.

The Ophidian Tick-parasites, like those of mammals, birds, lizards, and tortoises, appear to be in many cases the means of transmission of protozoal infections from snake to snake.

The Tongue-worms (LinguatulidÆ) are, without doubt, of the greatest possible interest. Their systematic position has ever been a puzzle to zoologists, and even now is a matter of controversy. They have been looked upon as Hirudinea by Winsberg (1765), Cestoda by Chabert (1787), Acanthocephala by Humboldt (1808), Trematoda by Rudolphi (1809), and Nematoda by Nordmann (1832). It was Van Beneden (1848) who first recognized their Arthropod nature, but he placed them amongst the Crustacea. SchubÄrt (1853) suggested that their proper position is amongst the Mites (Acarina), and Leuckart (1860) adduced important anatomical and embryological evidence in support of this view, which was confirmed by Railliet in 1883 and by Sambon in 1910.

No less than three out of the four genera of Linguatulids so far established are represented by species parasitic on snakes. They are the genera Porocephalus, Reighardia, and Raillietiella.

The genus Porocephalus is of special interest, because some of its species, such as Porocephalus armillatus, a parasite of African Pythons (Python regius, P. sebÆ) and Puff-adders (Bitis arietans, B. nasicornis, B. gabonica), and Porocephalus moniliformis, a parasite of Oriental Pythons (Python molurus, P. reticulatus), are, in their nymphal stage, deadly parasites of mammals, including man.

The genus Reighardia was established by Professor H. B. Ward, in 1899, for a Linguatulid of gulls and terns, first described, in 1861, by De Filippi. In 1910 Sambon included in this genus other similarly structured Linguatulids from crocodiles, monitors, and snakes.

The genus Raillietiella was established by Sambon in 1910 for a Linguatulid (Raillietiella boulengeri) of the African Puff-adders (Bitis arietans, B. gabonica). Amongst the characters of this genus is one of great structural and phylogenetic importance—viz., the position of the female sexual orifice at the anterior end of the abdomen, whilst in the other known genera it is at the posterior extremity.

According to Prowazek, Sambon, and Laveran, the Ophidian Linguatulids, which live as blood-suckers in the air-passages of their hosts, are able to foster and transmit the hÆmogregarines of these hosts.

Acanthocephala.—The early encysted stages of several species of Thorn-headed worms (Acanthocephala), belonging to the family EchinorhynchidÆ, have been reported from snakes belonging to very different genera, such as Boa, Tropidonotus, Zamenis, Drymobius, Xenodon, Dipsadomorphus, Oxyrhopus, Erythrolamprus, Diemenia, Naja, Elaps, Vipera, Lachesis. Their further development probably occurs in ophiophagous birds. Thus, Echinorhynchus oligacanthoides, Rud., the immature stages of which occur encapsuled within the body cavity of Lachesis lanceolatus and other neotropical snakes, when adult is found attached to the intestinal mucosa of Milvus bidentatus.

Nematoda.—The roundworms (Nematoda) so far described from snakes belong to the families AscaridÆ, StrongylidÆ, TrichotrachelidÆ, and FilariidÆ. Some of the genera belonging to these families, such as Cucullanus, Nematoxys, Oxysoma, are as yet represented by a single species in a single host; others, such as Ascaris, Polydelphis, Heterakis, Strongylus, Diaphanocephalus, Physaloptera, Trichosoma, number already several species more or less widely distributed.

Eelworm infection (ascariasis) is very common in snakes, and not infrequently the infection is a heavy one; Sambon twice found over fifty specimens of Polydelphis in Puff-adders (Bitis arietans). This investigator has shown that the snake eelworms undergo an encysted stage of development within the body cavity of their hosts before migrating into the intestinal lumen for the purpose of fertilization and oviposition. Thus, Redi was quite right in considering the immature, encysted forms found in one of the livers of his double-headed Asp as belonging to the same species of eelworm (Ascaris cephaloptera) as that which the snake harboured in its intestine.

Professor A. Railliet, whilst examining specimens of Polydelphis which had been preserved for nearly two months in a 3 per cent. solution of formalin, found that the ova within their uterine tubes had undergone development, and still contained living embryos; indeed, some of these hatched under the microscope, and moved very actively in the preserving fluid. This is in no way surprising, because even after several years of preservation in formalin solution the embryos of other species of eelworms (Ascaris equorum, A. marginata) have been found in a living condition.

Trematoda.—The Flukes (Trematoda) of snakes, so far described, belong to the following genera: Agamodistomum, Astiotrema, Brachylaimus, Cotylotretus, Dicrocoelium, Diplodiscus, Distoma, Halipegus, Lecithodendrium, Metorchis, Opisthogonimus, Opisthorchis, Plagiorchis, Saphedera, Telorchis, Tetracotyle, Zeugorchis.

Cestoda.—Save a few larval forms (Cysticercoides, Piestocystis, Sparganum), the known tapeworms (Cestoda) of the Ophidia belong to the genera Bothridium and Proteocephalus.

Protozoa.—Numerous species of HÆmogregarines have been described from snakes. As a rule the forms seen in the peripheral blood are sporonts, the schizogonic cycle occurring in the lungs. The sporonts do not greatly alter their host cells; they are invariably doubled up within a more or less thick capsule. Some species show a marked sexual differentiation, others not. Trypanosomes, SpiroechaudinniÆ, and PlasmodidÆ have also been described from the blood of various snakes.

Within the alimentary tube have been found species of Trichomonas and Caryospora.

Bacteria.—Acid-fast bacilli have been described in tubercular lesions found in snakes by Sibley, Gibbs and Shurley, Shattock, Hausemann, and Sambon.

The so-called “canker,” which so frequently develops in the oral cavity of captive snakes, is also a bacterial disease, due to a specific bacterium of thick, rod-shaped form.

Acanthocephala.

Nematoda.

Trematoda.

Cestoda.

Nematoda.

Trematoda.

Acanthocephala.

Trematoda.

Cestoda.

Protozoa.

Acanthocephala.

Nematoda.

Trematoda.

Cestoda.

Acanthocephala.

Nematoda.

Trematoda.

Protozoa.

Protozoa.

Nematoda.

Cestoda.

Protozoa.

Protozoa.

Nematoda.

Trematoda.

Arthropoda.

Acanthocephala.

Nematoda.

Protozoa.

Nematoda.