OF FOREST-TREES. 



135 



If, as sometimes, it proceed from the baking of the earth about the stem, CHAP. Vir. 

 lighten and stir it. ^.--^^Y'"^ 



Sixthly, The teredo, cossi, and other worms, lying between the body 

 and the bark, (which they separate,) poison that passage to the great pre- 

 judice of some trees ; but the holes once found, they are to be taken out 



manner as the yolk in an egg, becoming the placenta, prepares the nourishment, and sends 

 it by the navel-string to the chick. Linn. 



The annexed plate represents the egg of a hen on the fourth day of incubation. Fig. i. 

 The containing and contained parts, as they appear upon the removal of the forepart of 

 the shell. Fig. ii. The shell. Fig. iit. The two membranes which line the inside of the 

 shell, and inclose the whole contents, a. The shell, h. The inner membrane, c. The 

 cavity formed by the membranes, in which a portion of air is inclosed. Fig. iv. The 

 white, which serves for the nourishment of the chick during incubation. Fig. v. The yolk, 

 with the speck of life and its blood-vessels, a. The yolk. h. The cicatricula, containing 

 the speck of life. c. c. The chalazae, or twisted extremities of the membrane that sur- 

 rounds the yolk. — If we compare these chalazae to the extremities of an axis passing 

 through the yolk, that sphere will be found to be composed of two unequal portions, 

 its axis not passing exactly through its centre. And as the cicatricula, with the speck of 

 life, is always placed on the side of the smaller portion, it follows that in all positions of 

 the egg, during the first five days of incubation, it must be uppermost, and consequently 

 nearest the hen ; for the yolk is a body specifically heavier than the white with which it is 

 surrounded. 



It is wonderful to observe the attention of Providence to the infancy of animal life ; but 

 our wonder is turned into adoration, when we observe the same goodness continued through 

 all tlie stages of animal existence. It is in the form of instinct that the finger of God 

 operates during the advanced periods of animal life ; a principle, that never ceases to act 

 for the preservation, as well as continuation, of animated nature. 



From the foregoing observations, it is evident that the seeds of all vegetables may be 

 considered as eggs, from which the respective species are produced. Now, daily experience 

 teaches us, that no egg can produce an animal, till it be impregnated or fecundated by 

 the male : a hen indeed will lay eggs, but they will prove abortive, unless they are im- 

 pregnated or fertilized by the male. That generation precedes the birth, appears through- 

 out universal nature. In quadrupeds it does without doubt : but in fishes, it is supposed by 

 some that generation follows or comes after the birth or exclusion of the eggs, and that the 

 male sperm is emitted upon the eggs after they are excluded from the matrix of the female. 

 This is demonstrable in salmon during the spawning season. 



Physiologists have entertained a variety of opinions concerning generation. After 

 rejecting the effervescences, precipitations, and other ridiculous notions of the ancients, 

 they now seem to acquiesce in two opinions. The first is that of the great Hervey, who 

 supposed that in the speck of life, or cicatricula, the entire rudiments of the future foetus 

 were present, perfect in all its members, and that it was only requisite that the male 



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