There can at all events be no doubt that they were developed from the genera] formative mass of blastema, which surrounds the aorta in the fetus, as described by Professor Goodsir;[1] and that therefore they were morphologically as well as physiologically to be classed with the thymus.[2] This gland, as well as the thyroid, was largely developed in this specimen, and the arrangement Of the two glands coincided very exactly with the description given of them by my friend Mr. Turner.[3]
The lymphatic glands generally throughout the body were largely developed; so largely, in fact, at either jaw angle, as to simulate the appearance of a large submaxillary gland.
The spleen was, as has been so often described, curiously multifid.
All of these ductless, all of these lymphatic, glands were richly supplied with blood vessels; all, alike and jointly, laboured at the elaboration of the constituent elements of the vast mass of this cetacean's blood. They enabled it thus to support a high standard of temperature in an excellent conducting medium, and they supplied all the calls for rich and refined aliment which a brain equalling in this case one-sixtieth of the weight of the entire body, made upon the nutritive fluids. They may be taken as illustrations of "tautogeneous growths" of the first of our two classes.
Many of Mr. Paget's instances of complemental nutrition, Mr. Darwin would explain as the results[4] of hereditary transmission, with modification, and there can be little doubt that of the two hypotheses the latter will, to many minds, seem to suit the better with such instances as the four rudiments of nails on the fun of the Manatee, or the equally rudimentary teeth in the Ruminant's intermaxillaries, or of the representatives of the Polian vesicles in the Arenicola.
But many of Mr. Paget's instances cannot be brought under this head, and constituted as our minds are, we cannot but read them as he has done.
Mr. Darwin, on the other hand, himself[5] admits that there are many instances of correlated growths of which our reason can give no rationale, either as subserving ends, or as confirming to type, or as speaking of parentage, or as working up into structure what would else be waste and excretory; for which in other words it can assign neither final nor formal, nor material cause. I would instance in addition to those he brings forward, the correlations of growth witnessed in Morbus Cæruleus betwixt a malformation of the heart and
- ↑ Phil. Trans. 1846, p. 638.
- ↑ In the common Shrew, however, two bodies are to found, floating loosely in the abdominal cavity, but anchored each by a process of mesentery which is attached just where these bodies in the Porpoise lie fixed; and that they are connected with the lymphatic or rather with the lacteal system, an examination of a Shrew, which has died whilst digesting, will leave no doubt.
- ↑ Transact. Royal Soc. Edinburgh, Vol. XXII. Part ii.
- ↑ Origin of Species, p. 453-454, 1st edit. pp. 486-487, 3rd edit.
- ↑ Origin of Species, pp. 145, 197, 1st edit.; pp. 162, 217, 3rd edit.
