Having in the next place removed the Lumbricus with a pair of forceps, and having washed it under a current of water, I snipped off the lower end of the body, and allowed some of the intestinal contents to escape on a clean glass slide for separate microscopic examination. Immediately, to my satisfaction, I found that the fæcal contents displayed a large quantity of my strongyle ova, enclosing still living embryos, and in addition several free embryos presenting characters which declared that they were from the same source. Clearly they had been ingested by the earth-worm along with its ordinary food. One or two of the embryos were conspicuously larger than their fellows, but the structural changes they had undergone were not so marked as to lead me for a single moment to associate them with any of the various sexually-mature worms which have been described as normally infesting the earth-worm. I had no doubt whatever that such slight structural changes as were now discernible had resulted from growth and development consequent upon this accidental admission into the body of the intermediate bearer which might or might not prove to be its legitimate territory. It will be seen that subsequent observations tended to affirm the truth of this view. I made a careful examination of one of these larvæ, whose active movements were such as to render the process exceedingly tedious. The earth-worm itself (or rather its unequal halves) was placed in a fresh watch-glass containing ordinary mould. The larvæ or embryos obtained from the earth-worm now measured about 1/80 of an inch in length, their heads exhibiting a short and simple chitinous buccal tube, whilst their tails were somewhat more pointed and bent upward. The somatic granules were more crowded, rendering the position of the intestinal tract more marked, though, as yet, the differentiation gave no indication of the formation of a distinct intestinal wall. There was no perceptible increase of thickness of the body of the embryos. The results thus far naturally encouraged me to procure some fresh earth-worms for experimental purposes.
On the 26th of October I found that the halves of the earth-worm were alive, and I left them undisturbed in rather dry mould, freshly added. To a watch-glass containing newly sifted earth and embryos I added a fresh garden-worm, which was rather sluggish from the cold; and in the original jar I placed another smaller and very active earth-worm obtained the same morning. Finding the soil in the jar congenial, this lumbricus soon buried itself. Another and larger earth-worm subsequently added refused to follow this example. It was therefore removed from the jar. Believing the fine and artificially prepared soil to be still much too moist, I caused further evaporation; and I afterwards found that the thicker the mud the more suitable it proved as a residence for embryonic nematodes and earth-worms alike.
On the 27th I found the small earth-worms in the jar burrowing freely and throwing up fæcal casts. From one of my watch-glasses the worm had escaped, its place being occupied in the meantime by an actively crawling Julus. I put a second Julus, obtained from the mould in the fern jar, to form a companion (in view of other experiments), and I also added a fresh earth-worm, covering all by another inverted watch-glass, which I thought would prevent their escape.
In the next place I examined the halves of my original experimental earth-worm. They were scarcely capable of motion, but retained a certain amount of vitality. The tail was the more active half, and unfortunately it was soon afterwards lost. Carefully washing the superior half, and transferring its contents to a glass slide, I immediately detected under the microscope a large number of embryos. They were in a state of marked activity, the largest having increased to about 1/50″ of an inch in length, whilst their structure had become correspondingly advanced. Here, again, there was no room for doubt as to their source, especially as they individually displayed different degrees of organisation, all answering to one and the same embryonal type. I now observed a distinct œsophagus, the rest of the intestinal tract being still more conspicuous than heretofore, though, as yet, no true cells marked the limitation of the stomach and chylous intestine.
After an hour’s immersion in cold water some of the larvæ became much less active, whilst others were motionless, so that I feared all were about to perish. In the hope of keeping a few of them alive I now added to the slide some finely sifted grains of mould, placing the slide under a small bell jar which protected some of my ferns. The remains of the moribund earth-worm were also covered with mould.
Other larvæ, derived from the earth-worm, were placed on the moist pinnæ of a living fern-frond which supported small drops of water, for by this process I hoped in some measure to imitate the dew which naturally condenses on the grass and fodder of our low-lying fields. At 3.15 p.m. of the same day (27th) I also examined a fresh worm pellet from the jar, and found it to contain living strongyle embryos, which as heretofore had not exhibited the slightest advance either in respect of size or structure.
At noon on the 28th I again sought for the larger larvæ, first of all on the slide covered with fine earth, and afterwards within the remains of the upper half of the original earth-worm. On the slide I could detect none, but within the intestine of the worm there were still two living larvæ left, whose characters corresponded precisely with the largest that I had previously obtained from the same source only the day before. They had undergone, however, no further change in structure, and their measurements remained precisely the same.
At 12.30 p.m. I snipped off two or three of the terminal fern-fronds on which I had placed a few advanced larvæ. On examination under the half-inch objective I immediately detected one of the larvæ cruising about most actively. On adding a drop of water it soon rushed across the field of the microscope, its movements being thoroughly eel-like. The size of this larvæ had so much increased that it was now visible to the naked eye, measuring, indeed, as much as 1/30 of an inch from head to tail. Moreover, its organisation had advanced in a marked degree. Thus, the digestive organs were better defined, and on one side of them there appeared a regularly arranged congeries of cellules, forming the commencement of the reproductive organs. As yet, however, I could not pronounce as to the sex.
At 1.45 p.m. I again examined a few grains of earth from the jar, when I at once noticed five or six active embryos whose structure failed to show the slightest advance upon that originally described. It was evident that the jar contained thousands of them; and since no ova were found, it became probable that all their embryonic contents had escaped to swell the number of free larvæ, leaving their very delicate envelopes to perish. I think I had hit upon the most suitable degree of moisture favorable to this result.
In the next place I sought for the earth-worm that had been placed in the infested soil between two watch-glasses. It had escaped. This obliged me to transfer the mould to a rather wide-mouthed and open phial, in which four more fresh lumbrici were placed. I feared the closing of the bottle would be detrimental.