celebrated chapter on the snakes in Iceland, and say simply that there are in Sphærularia, no muscles, no nervous or circulatory systems, and no intestinal canal.
A priori it would seem almost impossible that an animal could exist without these organs. Muscles, however, would be useless, or even destructive. So long as the Sphærularia remains quiet, the Bee does not seem incommoded by its presence, which perhaps produces scarcely any abnormal sensations; but if the parasite, being so large in proportion to its victim, were to move about, it would probably so affect and disarrange the viscera of the Bee, that the poor insect would be quite unable to pursue its usual avocations, and would quickly perish. The female Sphærularia being thus, when full-grown, reduced to a merely vegetative existence, the nerves of motion and of sensation must, of course, be useless, and would soon become atrophied. Under these circumstances, however, it might have been expected that the digestive organs and their nerves would have been highly developed. That, on the contrary, these organs are also absent, is probably to be explained by the fact that the animal is bathed on all sides by the blood of the bee, and thus lives in a medium which is highly organized, and requires, probably, scarcely any further elaboration.
Moreover, although this absence of certain important parts is carried to an extreme in the present animal, we find in other Nematoids a considerable approach to the same condition. Indeed, until within the last few years, we had scarcely any reliable knowledge of the nervous system in any of the Nematoids; lately, however, it has been figured and described at length in several genera, as, for instance, in Strongylus, Ascaris, Oxyuris, Gordius, and Mermis; but even in Van Beneden's Prize Memoir, "Sur les Vers Intestinaux," the nervous system is scarcely so much as mentioned; and it seems very doubtful whether the filaments referred to by Meissner in Mermis as nerves, do not rather belong to the muscular system; while the so-called supra-œsophageal ganglion is asserted by Schneider to be really the œsophagus.
In the Nematoids generally the intestinal canal is a straight tube, reaching from one end of the body to the other. In Mermis and Gordius,[1] however, we meet with a totally different and very abnormal type, which it is unnecessary for me here to describe. It is sufficient to say that, whereas in these two genera there is no stomach, and that, while in Mermis the œsophagus is small, and in Gordius quite rudimentary, I have in the mature female Sphærularia been unable to detect any trace of them at all.
The same is the case with the muscular system. I have often opened the body along one side, and then stretched out the skin. In this manner it may be examined with a high power; but I have never been able to see any structure in the least like muscular filaments. The entire absence of motion confirms this view.
- ↑ The intestinal canal is quite short also in some other worms, as, for instance, in Nemertes.
