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Show 1895.] HYDBACHNID FOUND IN COBNWALL. 187 it overlies and touches the ventriculus for a considerable distance, yet I am utterly unable to find any sign of a communication between the two. There is not any point where the outer coat of the excretory organ becomes vague as in Henkin's Trombidium. I have carefully examined sections, cut in all directions, with high powers, and the tunica propria appears continuous and most distinct everywhere, and in some specimens the two organs do not quite touch anywhere, there being a distinct space between with connective tissue joining them. I know how difficult it is sometimes to detect communications, and therefore I will not absolutely deny that anything of the kind exists: but I am decidedly of opinion, however improbable it may seem, that it is true that the mid-gut ends blindly, and that the excretory viscus winch ends in the anus-like opening (fig. 10, A.) has not any communication with the mid-gut. The improbability is diminished when we consider that these creatures do not swallow any solid food, but live entirely by suction, feeding on the blood of other minute creatures which they capture ; still, of course, a Spicier or a Gamasid lives in the same way, but has a distinct hind-gut and anus. In the present instance, however, I have not ever seen food in the organ, as we should expect to do if it were in direct communication with the ventriculus ; I find the white excretory matter and that only. With regard to the homologies of the organ, if it were not for Schaub's species, 1 should say that it appeared to m e that the anus-like opening was the true anus, and that the excretory organ which leads to it was the homologue of the hind-gut; although in consequence of the nature of the food, or for some other reason, the hind-gut had become severed from the mid-gut and had lost its function as a hind-gut, assuming that of the Malpighian vessels found in Gamasidae, &c. I have not ever seen Schaub's species; but if we can rely, as w e naturally suppose we may, upon his investigations, which I believe were conducted in Professor Cohn's laboratory at Vienna, then the presence in so closely allied a species of a second anal opening, and of a well-marked and functional hind-gut, in addition to the excretory organ and opening, would seem to prove beyond question that in other species, such as the present one, the hind-gut and anus have become obsolete, and that the excretory organ is of the nature of a Malpighian vessel, or at all events of the organs which bear that name, whether properly or not, in the Gamasidae, &c, and in many other Arachnida, e. g. Mggale, & c , although it discharges to the exterior instead of into the hind-gut between the colon and the rectum, which is the point of discharge in Gamasidae, &c. The form of the excretory organ (fig. 15, and figs. 14, 23, E.) is very much that shown by Schaub, viz. an elongated sac with a rounded, caecal, anterior extremity, varying and irregular in its diameter, but widening out so as to form a pyriform expansion before it suddenly narrows to reach its point of discharge. This widened part is generally compressed dorso-ventrally by folding and compression. These folds are quite irregular and do not |
