The palpebral and oculomotor apparatus in fishes : observations on morphology and development / by N. Bishop Harman.

  • Harman, Nathaniel Bishop, 1869-1945.
Date:
[1899]
Catalogue details

Licence: Public Domain Mark

Credit: The palpebral and oculomotor apparatus in fishes : observations on morphology and development / by N. Bishop Harman. 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.

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    to a greater or lesser degree, by delicate connective tissue which •can be seen tearing up as the flap is pulled off. In some fishes the connection is so slender that the separation can be made and the ‘ space’ injected by forcing fluid through a hole made in the outer layer, when it will be demonstrated that the ‘ space ’ has no connection with other subcutaneous tissue. In diseased con- ditions of captive fish this potential ‘ space ’ frequently becomes actual and distended with gas; a like condition may affect loose tissues elsewhere. I have seen a similar condition in freshly ■caught Pouter-whitings, and I am informed that this is always the condition of this fish immediately on removal from the water, but there is no appearance of it in the healthy free- swimming fish. In Eels the layer is removable with some difficulty, and then the bulbar part of the cornea can be stripped off layer by layer of transparent connective tissue. The outer corneal layer is sepai-able in almost every species of sea-fish, excepting those of voracious habits. It is not separable in those whose habitat is fresh or fresh and salt water, thus:— It is inseparable in Selachoidei, Batoidei, Holocephala, Chon- drostei, Perciformes, Cotto-scombriformes (ex. Lophius), Mu- giliformes, Cyprinina, Esocidte, Salmonidae (ex. Smelt), and Clupeidte. It is separable in Gastrosteiformes, Gadoidei, Pleuronectoidei, Mimenidte, Syngnathidse, and Gymnodontes. The only exceptions to the generalisation from habitat are ■Smelt and Stickleback. Both these fish were very small and soft, being winter specimens, so that the exception may be accounted for by ill-condition. The Eels appear exceptions, but the remark on the mode of separation for these fish shows them to be on the border line. The histology of the cornea in Cod, Eel, and Trout has been treated by Lightbody (20, p. 40), who .shows there is in Cod a layer of muco-areolar tissue dividing the cornea into two parts. I have made similar observations on the Plaice, which show that the proper substance of the cornea is not completely organised.