Fig. 329.—Ancylostoma duodenale: eggs in different stages of development. a to c, in fresh fæces; d, containing a larva, only in old fæces. × 336. (After Looss.)
Egg of Ancylostome appears to have a single contour. Under high powers this appears double, but they are the outer and inner surface of the true (chitinous) egg-shell. Internal to this is the extremely delicate yolk-envelope, a kind of skin secreted by the egg cell around itself for protection. The function of this is probably to absorb water to swell and burst the outer chitinous shell. The embryos when hatched are termed larvæ.
Embryos which are ready to hatch have their bodies almost free from granules; others, though apparently mature, that have granules will not hatch.[318]
Fig. 330.—Ancylostoma duodenale larva on fourth day of culture on right; Strongyloides stercoralis larva on left. (After Leichtenstern.)
Larva.—Stage I: Average length, 25 mm. Maximum thickness in œsophageal region, 17 µ. Head end fairly blunt, from behind the anus (the tail) tapering in an uniform manner. Buccal cavity is characteristic, 10 µ to 12 µ by 1 µ to 8 µ, longer and narrower than the corresponding larvæ of Strongyloides stercoralis. Œsophagus “rhabditic” in character, i.e., it has three sections, but they are not so clearly marked off as in larvæ of the genus Rhabditis. The posterior bulb has a Y-shaped valve, the function of which, according to Looss, is to prevent regurgitation of food. The granules of the gut serve as a reserve of food, and are used up if the larvæ are starved. The genital rudiment consists of two cells half-way between the end of the œsophagus and the anus in the mid-ventral line. The larva lives on fæcal matter and grows to about 0·4 mm., then moult[319] I takes place in two days or more, the skin being ruptured by the activity of the larva.
Stage II: The larva is now in this stage, which does not differ much from the previous one. It grows to 0·5 mm. The mouth opening closes. The œsophagus elongates, becoming cylindrical or “filariform”; a new skin is formed underneath the old one, and in about a week moult II takes place.
Stage III: The mature larva remains enclosed in the old skin. Its movements are now much more active and of a boring character. Length is now 0·6 mm. This mature stage has been erroneously called the encysted larva, because there is no cyst secreted from its surface by the larva, but it is simply the old skin, which is not cast off, but is retained for purposes of protection, as the larva is free living, but casts it as soon as it assumes parasitic life again. From the egg to this mature stage is thus six to ten days.