On the alternation of generations; or, the propagation and development of animals through alternate generations: a peculiar form of fostering the young in the lower classes of animals ... / By Joh. Japetus Sm. Steenstrup ... Translated from the German version of C.H. Lorenzen, by George Busk.

  • Steenstrup, J. Japetus Sm. (Johannes Japetus Sm.), 1813-1897.
Date:
1845
Catalogue details

Licence: Public Domain Mark

Credit: On the alternation of generations; or, the propagation and development of animals through alternate generations: a peculiar form of fostering the young in the lower classes of animals ... / By Joh. Japetus Sm. Steenstrup ... Translated from the German version of C.H. Lorenzen, by George Busk. Source: Wellcome Collection.

    71/174 (page 63)
    covering them, and their long bodies will be found half floating as it were in the fluid, which occupies the space between the organs and which appears to be pure water, entering through the aqueducts or water-passages. Fig. A a represents two of these “ nurses’” a little magnified ; their great difference from the Cercarıe, and still more from the flukes is very apparent. Fig. 4 @ shows a similar individual more highly magnified, and also slightly compressed between slips of glass, which renders the vast number of Cercari@ within it more distinct. It is not only the outlines of this brood of Cercarie, which are seen in the “ nurses’’ thus compressed, but several of their internal organs as well, as for instance, the forked intestine and the liver. As regards the external form of these worms, it must be allowed that it is usually alike in all, unless they have suddenly contracted themselves, in consequence of some external irritation, and owing to which contraction they are sometimes scarcely recognizable from the alteration in their shape. However, the number of these creatures is so great, that they are crowded together on the walls of the water-passages, or in the cellular tissue surrounding the liver, kidneys, &., and on this account it not unfre- quently occurs that, even within the snail itself and before the worms have been touched, such contracted misshaped individuals are met with, recognizable only by the oblique projections on the posterior half of the body.* The “ nurses’’ usually present the appearance given in fig.4 a and 5. The body is cylindrical, and is furnished in most instances with a spherical, contracted head, which includes an oral cavity with very muscular walls, and a small circular mouth. Below the head is a sort of collar which abuts upon a depression, which according to the greater or less state of contraction of the animal, is nearer or further from the mouth. When the head is drawn towards the depression, the collar projects straight out * Baer has figured one in this condition. Nova Acta, Acad. Nat. Cur. tom. xii. tab. 31. ;