44 An Introduction to Zoology. 



trochus and turbo, we find a sort of middle term between tlie monoecious 

 and dioecious plans ; for here each individual possesses, like the monoecia, 

 both the proliferous and fecundating systems. But like the dioecia, the 

 combined influences of two individuals are required, each- reciprocally 

 fecundating the other, and each becoming in turn proliferous. In the 

 univalves of t!ie buccinoidal family, (Buccinum raurex, &c.) as in all the 

 superior orders, insects, Crustacea, fishes, reptiles, birds, and mammalia, 

 the plan pursued is strictly dioecious 5* the only differences being, that in 

 some instances, (fish and reptiles) the eggs are fecundated after their ex- 

 clusion from the parent body, and in others, (insects, birds, and mammalia) 

 before. 



Having thus traced the whole series of the animal functions, as exhi- 

 bited in their mature state, it would be most interesting to give some 

 account of the light thrown by the most recent observations on tlie progress 

 of their original development in the germ included in the egg. The 

 effects of incubation in the egg of the domestic fowl, as they are the most 

 easily observed, so are they among the most beautiful illustrations of the 

 prospective contrivancss Oi" that providential care which gradually fashions, 

 ere yet the use of any one of them is possible, organs accommodated with 

 the most exact view to all the wants of a future state of existence, totally 

 dissimilar to that which then prevails. — " Whose eyes did see their sub- 

 stance being yet imperfect; in whose book were all their members written, 

 which gradually and successively were fashioned, while as yet there was 

 none of them." 



But this must be reserved for a future Essay. We shall propose also, 

 in the ensuing numbers, to follow up this general introduction, by a brief 

 account of the most important of the great divisions of the animal king- 

 dom, illustrated by a constant reference to the preparations contained in 

 the museum of the Bristol Institution, which will be found very copious. 

 We shall hope thus materially to add to the instructive usefulness of that 

 excellent institution, to develope all its resources as a rich local source of 

 supplying the most efficient means of physiological information, and to 

 extend the general interest in its adequate support and increase. 



* We have dwelt more particularly on the single order of bivalves and univalves, 

 because in this class we have illustrations of all the known combinations as to this 

 subject ; and it is important to observe the very wide deviations of animals in this 

 most important function, exhibiting so close an agreement in the rest of their 

 organization. 



(To be continued.) 



