Observations on the development of the medusæ / by John Reid.

  • Reid, John, 1809-1849.
Date:
[1848]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the development of the medusæ / by John Reid. 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.

    2/16
    As every part of their body is contractile, they can assume a great variety of forms. The more common of these are represented in PI. Y. figs. 1, 2, 3, 4 and 5. Though almost all of them are throughout of a grayish white colour, a few presented spots or patches of a purple colour, which were sometimes observed to dis- appear and reappear in the same individual. The tentacula are generally from twenty-two to twenty-seven in number, and when fully expanded are three or four times the length of the body. In one that I measured the body was ^\ths of an inch, and the tenta- cula ths of an inch in length • in another the body was |fths, and the tentacula /¥tlis of an inch in length. The mouth is very dilatable and varies much in shape, but is most commonly qua- drangular. When fully expanded it forms a round aperture oc- cupying nearly the whole of the disc (fig. 5); at other times its margins or lips are elongated and approximated so as to form a considerable quadrangular projection (fig. 2 b). Its more com- mon condition perhaps is that represented in fig. 3 a. The four round, equidistant and slight depressions placed be- tween the mouth and margin of the disc are represented in fig. 2 a. The body and tentacula of the larva are composed of two di- stinct layers, an internal and external. The internal layer chiefly consists of nuclei and nucleated cells (PI. VI. fig. 19) of various sizes, some of them containing a large number of nuclei; while the external is chiefly composed of a structureless substance with numerous minute nuclei disseminated through it. Numerous nearly elliptical and oval capsules (filiferous capsules), having a long thread or filament coiled up in the interior of each, are fixed upon the outer surface of the external layer, and in much smaller number upon the inner surface of the internal layer, where it lines the internal cavity or stomach. These capsules are most abundant upon the external surface of the tentacula. Pig. 20 is a highly en- larged view of a small portion of one of the tentacula, showing the filiferous capsules attached to its outer surface. These fili- ferous capsules vary much in size, but the largest are generally of a uniform size, nearly of an elliptical form, and about ^oVan inch in their largest diameter (PI. V. fig. 8). Several of these, de- tached in examining portions of the larva under the microscope, had hurst open at the smaller end, and the spiral thread projected through the opening and was uncoiled (fig. 9). In the entire capsule a rounded and narrow column passes from the smaller end, beyond which it slightly projects, in the direction of its longest diameter, nearly to its other extremity; and this column, to which the spiral thread is attached, protrudes from the interior of the capsule when it bursts. I have never observed these filaments projecting from the capsules when adhering to the surface of the body, unless when subjected to pressure, but it is difficult to use the