1821.] Dr, Palis on the Physialog^ of the Egg. 353 



pagate their species by the intervention of the egg, nor is such a 

 mode of generation either accidental in its occurrence, or unim- 

 portant in its operation; had the v»'inged inhabitants of the air 

 been viviparous, the burden of gestation would have impeded 

 the action of their wings, and have so far increased their gravity 

 as to have rendered them incapable of the exertion of flight : 

 the rigid and unpHant coverings of crustaceous animals would 

 have opposed the expansion necessary for th^e developement of 

 a foetus ; and it is evident from the structure and habits of the 

 tribe of serpents, that if they had been viviparous, their offspring 

 must have suffered materially from the tortuous flexionS', and 

 friction necessarily attendant upon their progressive motions ; 

 and, lastly, the multiparous^ nature of inse^^ts and fishes at once 

 convinces how im^provident it would have been to engender thena 

 by any other mo4e than that which nature employs. 



The eggs of the ovipari admit of an evident division into two 

 classes, which I shall denominate, 1. The Perfect ; and 2. The 

 Imperfect, The former, which are deposited by the aves, and 

 some genera of amphibia, are completely covered by a hard shelly 

 or membrane, and receive no additions after their exclusion; 

 while the latter are deposited by most pisceSy and in general 

 constitute a soft mass (favago), not being protected by any 

 external involucre. The observations contained in this memoir 

 relate more particularly to the egg of birds : their history, how- 

 ever, comprises whatever is interesting or important in the germs 

 of inferior animals. 



In order that I may be better able to form a systematic rela- 

 tion of those new facts and opinions which I wish to submit to 



ties; the aphides lay eggs at the end of autumn, when the young produced from thaaa 

 m the spring are viviparous during the whole summer ! The cocci hatch their eggs before 

 their exclusion, and the young force their way through the abdomen of their mother* 

 The onisci carry their eggs in a particular receptable, from which, in process of time, 

 the young make their escape. The hijjpabosca brings forth neither eggs, nor larvae;, but 

 those already gone into the jpupa state ! The lacerta salumandra brings forth young, 

 complete in every part, but still enclosed in an egg. 



* Reaumur ascertained that a single queen bee had laid in the months of March and 

 April 12,000 eggs; and Lewenhoeck found that the mmca carnaria deposited 144 

 eggs, from which, in one month, were produced as many flies ; so that supposing one- 

 half of these to be females, there would be in the third month 746,490 flies. The amaz- 

 ing fertility of fish may be illustrated by \hQ gadus morlma^ the cod fish, which will 

 deposit among the rocks 9,000,000, or 10,000,000 of eggs ; and again, \hefcrcajluvla» 

 tills produces in April and May not less than 300,000 ova ! Dr. Baster says that he 

 counted 12,144 eggs under the tail of a female lobster, besides those that remained in 

 the ovarium unprotruded. I have frequently examined the ova of the lobster, and 

 there is one circumstance that, perhaps, deserves notice ; each ovum upon examination 

 will be found to be hexagonal in its form. If we were inclined to be eager on the sub- 

 ject of final causes, we might at once conclude that this form was the one adopted, as 

 affording facility of packing the greatest number in the least possible space, and we 

 might adduce the structure of the honeycomb as an illustration : the fact, however, i& 

 simply this ; that the ova, like all yielding bodies, assume the polyangular form, from 

 the mutual pressure which each sustains from its neighbour. Every person must have 

 observed the hexagonal bubbles upon the surface of porter and other liquors, from a 

 similar cause. 



New Series, vol. i. z 



