Abstract of a lecture upon the classification and structure of the leech : delivered before the members of the Pharmaceutical Society / by H. Letheby.

  • Letheby, H. (Henry), 1816-1876.
Date:
[1844?]
Catalogue details

Licence: Public Domain Mark

Credit: Abstract of a lecture upon the classification and structure of the leech : delivered before the members of the Pharmaceutical Society / by H. Letheby. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    7/12 (page 7)
    delicate membraneous films and rings which are to be found float- ing in the water with the leeches; when unravelled they present a perfect cast of the animal. They have an amorphorus structure, though, doubtless, in an early condition they were composed of plaster epithelium. One of the common causes of disease among leeches, is an inability to throw off this tunic, and we may remedy the evil by placing small pebbles, or a piece of very porous sponge, in the water for them to crawl through. Beneath the epiderm is the derm, or chorion, or true skin : it is a highly contractile reticular tissue, inclosing numerous oblong pigment cells, arranged with their long axes perpendicular to the surface, to or from which they are capable of being moved by the partial contractions of the derm ; and in this way,under particularcircum- stances, the colour of the skin is altered. The derm is excessively vascular, receiving most of its blood from the lateral vessels, and no doubt it performs a very important part in the function of respira- tion. The skin upon the inferior surface of the body is lubricated by a secretion, which is poured out from a number of very minute pores. Theyoccur at the abdominal margin of every fifth ring (figs. 4, e, and 5), and lead to small vesicles (fig. 6, c), which Duges and others have very erroneously regarded as pulmonic sacculi; they are merely the recipients of a mucus formed by a set of looped glands, which lie upon and cross the lateral vessels (figs. 6, b, and 12). 2. Muscular System.—The principal muscles lie immediately beneath the skin, and are ar- ranged in three planes or layers, namely an ex- Fro. 4. Openings of the tiiHinul nnrl abdominal mucous Fia. 5. ternal tTansverse,amiddle oblique, and an inner longitudinal. There is another and more internal perpen- dicular series, which serves to keep the viscera in place. The suck- ing discs are also provided with ra- diating and circular fibres,but they are only prolongations of the longi- transverse muscles, elands. Other special muscles, to be de- scribed under the digestive system,have to do with the movements of the jaws and the act of suck- ing. The three first set of muscles are the principal agents of progression: thus, when the posterior disc has been fixed, the contractions of the trans- verse muscles will prolong the anterior extremity. Abdominal snrface of while the oblique Can effect a movement to either di.^ ^pile^o'rdo'^ : then the leech, having attached the mouth (c)penU;(rf)vaginal sucker, and loosened the posterior one, contracts opening;; {e, mucus .1 1 • i- 1 • 1, ■ opcninss. the longitudinal set, especially on the abdominal