436 REPORtT—1905. 
industry.— Artificial hatching as used in the early days of the industry.—Present 
methods of rearing the chicks.—The principal diseases of the birds.—The present 
different methods of farming them,—The improvement of the breed by selection 
to obtain better feathers.—The growth of the export of feathers and the range of 
values.—The habits of the birds when sitting — Whether the innate wildness of the 
birds is lessened in the offspring of domesticated ostriches,— Prospects of the future 
development of the industry in South Africa, and of its being successfully de- 
veloped in other countries, 
5, The Réle of Mucus in Corals. 
By Professor J. EF. Durrprn, Ph.D, 
Under ordinary conditions the outer surface of coral polyps is covered with 
a thin continuous layer of mucus, in which objects falling upon the polyp become 
embedded or entangled. 
When first exuded the mucus is thin and watery, but later becomes more con- 
sistent. From time to time it is broken up into shreds and patches, which are 
removed from the surface of the disc by the ordinary exhalent currents from the 
stomodzeum, along with any foreign particles embedded. 
Nutritive substances and extractives placed upon the polyp increase the amount 
of mucus exuded, and also result in an opening of the mouth and the institution 
of an inhalent stomodzal current, by reversing the dominant outward beat of the 
stomodeeal cilia. 
The mucus exuded as a result of nutritive stimuli is drawn down the stomo- 
dzeum by inhalent currents in the form of distinct streams, and carries with it 
whatever substances, nutritive or non-nutritive, are embedded or entangled in it. 
Ingestion in coral polyps is thus purely mechanical, depending upon what- 
ever substances are capable of producing an inward beat of the cilia, the opening 
of the mouth, and the exudation of mucus. An inhalent current being established, 
objects are carried into the polypal cavity without regard to their nutritive value, 
and independently of any peristaltic motion on the part of the stomodzum. 
In the ordinary activities of coral polyps inhalent currents may be occasionally 
instituted independently of any external stimuli, and these carry with them any 
inert objects resting upon the disc. 
Mucus is of much importance in the protection of the polypal surface from 
foreign objects; it assists in keeping the surface clean, and also in the entangle- 
ment and ingestion of prey and food substances. 
6, Report on the Occupation of a Table at the Zoological Station, Naples, 
See Reports, p. 18!. 
7. Report on the ‘ Index Animaliwm.’—See Reports, p. 185. 
8. Report on the Influence of Salt and other Solutions on the Development 
of the Frog.—See Reports, p. 175. 
9. Interim Report on the Colour Physiology of the Higher Crustacea. 
See Reports, p. 187. 
10 Fifteenth Report on the Zoology of the Sandwich Islands. 
See Reports, p. 186. 
