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.

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    body, through which a fluid containing numerous glo- bules is expressed. I must suppose with Siebold, that this is the proper excretory organ of the Dzstoma, which thus obtains an exit. For it cannot be doubted that the fluid secreted and contained m this organ is of an entirely different nature in the Distoma to that in the Cercaria or its “ nurses” and “ parent-nurses,” since in the former it is rejected, and in the latter retained in the body. When the Cercaria is buried in the skin of the snail, it apparently secretes from its whole surface a very large quantity of slime, in which the animal, which we recog- nize as a distoma-larva, 18 in continual motion around the same point; and as the mucus gradually hardens, a case is as it were formed around it (fig. 44). The walls of this pupa case appear to be thickened by a delicate membrane, which is shed doubtlessly from the body of the animal itself, since the spiculum mentioned above is always found to be cast off, and to be stationary at some part or other of the walls of the cyst, although during the circular movements of the larva within the case it had been carried round from side to side together with it. The detached spiculum is afterwards covered over, and walled off by a distinct layer of mucus. (Compare 6 in figs. 4d, 4 e, and 4 f.) In a few hours after the /arve or Cercarie have af- fixed themselves to the skin of the snail, nearly all of them have assumed the pupa state; and the oval pupe may be placed so close to each other on (the back [xacken] and edge of the mantle of the snail) that a portion of the skin viewed under the microscope resembles, in miniature, a pavement composed of oval pebbles; and this is the case not only in snails which have been kept in glasses and in a small quantity of water, and consequently ex- posed to great numbers of their enemies, but also in those taken from pools of water mm the natural state. After entermg the pupa state, the animal appears to shrink away from the sides of the case, so as to leave a