Every living thing passes something of its life essence on to its offspring and in so doing perpetuates itself in a continual stream of existence, and as there are many grades and types of life so there are many ways in which this is accomplished. In all cases the life essence passes from adult or old bodies to new bodies or vehicles in a rhythmic cyclic process we may for the time being class under the general term of reimbodiment. When in any stock of life this series of rebecomings ceases, that particular branch of life-form becomes extinct, and the indwelling monad seeks reimbodiments in other houses of life. By reimbodiment we mean far more than the continual reproduction of physical forms, for these are but the clothes which the inner evolving entity for a time wears.
The phase of reimbodiment by which the identic life stream passes from parent to offspring in a continual coming again and again into physical life is known by the technical term of Palingenesis (Gr. palin, again + genesis, origin, coming into life). Examine a leaf on a tree. Notice the bud nestled at the base of the stem where it joins the twig. This bud grows as the leaf transfers more and more nourishment and vitality to it. In one sense the bud is its offspring, and when the leaf becoming old and useless falls to the ground, a new leaf will, in its season, unfold from the bud.
A seed is structurally a highly specialized bud which instead of producing a new leaf or twig, falls off the tree and unfolds into a new plant or tree which is both the offspring of the old and its re-imbodiment. But since plants have not yet evolved to the point of having an individuality or even a personality we cannot speak of them as having a continuation of consciousness. The stream of life simply flows on and on for ages upon ages, migrating and specializing with the changing climates as geological periods come and go.
The single-celled plants and animals continue their kind by simply dividing into two halves or cells again and again endlessly. With them, there is theoretically no death save accidental, no break in such overall consciousness as they possess; but only a continual re-entering a new cycle of activity much as we enter a new day with each new sunrise; but without our sense of individual consciousness. The cells of the human body follow the habits of their prototypes, the single-celled animals and plants, in multiplying themselves and in building the body in which we live. These single-celled creatures are in many ways analogous to the First Race of Man, who also reproduced by division, knew not death, and whose bodies were globes of iridescent light.
Every form of life above the single-celled plant or animal is more or less complex according to its stage of evolution; and so the different materials or elements composing the body have somewhat different habits, according to the kingdom of nature from which they are drawn.
Man is composed of many kinds of life. The mineral is represented in his bones and in the many kinds of mineral salts found throughout his tissues. The vegetable kingdom is represented by certain types of cells, in the bacterial flora without which he could not assimilate food, in the trace of chlorophyl present in the red blood corpuscles, and lastly in the hair and nails. Including all these is the animal body which provides the physical vehicle, without which man could not exist on this plane. Above this and dominating it is the thinker overshadowed by the spiritual and divine soul and ego. In fact, man is a microcosm — a miniature universe, as the ancients taught. To the lesser lives of which he is composed he is a galaxy of radiant starry atoms. But of his entire constitution and its complex life-cycle all that is known to the modern world is hardly one hundredth part of the whole.
The general lack of knowledge of the composite nature of man is illustrated by the following anecdote: Little Patsy went to her father, who was a well known biologist, and in great seriousness asked, "Daddy, are we animals?" He replied, "Yes dear. There is a mineral kingdom, a vegetable kingdom, and an animal kingdom; we are not minerals or plants but belong to the animal kingdom." The little girl, not completely satisfied, then went to her mother, who was an ardent Fundamentalist and asked, "Mother, are we animals, do we belong to the animal kingdom?" Her mother answered "No dear, we are not animals, we belong to the Kingdom of Heaven."
A Theosophist might have explained that as the human soul comes into reincarnation it gathers about itself materials, building blocks from all the kingdoms of nature, which it forms into a body in which it lives; and when the soul is through with its house of flesh and bone, the materials of which it was built go back to the departments of nature from which they were taken and are used again by other beings.
This gathering and dispersing of the life atoms — as a printer composes a page and when the printing is done redistributes the type into their respective boxes — was known in ancient times as Transmigration (L. trans, over + mlgro, migrate). The word means simply the changing of state or condition, as the life atoms forming man's body upon the death of the body pass into the kingdoms and planes of nature to which they are akin. This is the specific meaning of the word, but the principle is illustrated in a degree by the metamorphosis of many insects such as the dragonfly which passes from an existence in the water as a crawling nymph, to a life in the air as a glittering winged dragonfly. Other insects such as the cicada pass many years beneath the ground to later come forth, emerge from their skin, as beautiful winged insects.
On a vaster scale the monad peregrinating from plane to plane and from sphere to sphere in its journey from spirit to matter and return transmigrates as truly as do the life-atoms in their lesser range. But the reincarnating monad in its descent through the spheres puts forth soul after soul; gathering appropriate materials to itself, and then, when its term of activity on a particular plane is finished, withdraws much as the human ego is withdrawn into the heart of the monad upon completion of earth life. This habit of ensouling after ensouling is known by the name of Metempsychosis (Gr. meta, over + en, in + psyche, soul). And since the bodies on the superior planes are not bodies of flesh but of substances appropriate to each plane, the term Metensomatosis (Gr. meta, over + era, in + soma, body) is used. Of the different phases of reimbodiment, reincarnation applies only to the bodies of flesh assumed during earth life. Man having reached the status of a self-conscious being with awakened mind requires long periods of time between earth lives in other and higher spheres. Unlike the plant and animal he reimbodies only after long intervals of experience in the heaven worlds. Yet, as with the plant, the stream of his physical life essence continues from parent to child for ages.
The outstanding key to a study of the various aspects of reimbodiment is the focalizing or crystallizing effect of the indwelling monad which during its period of activity on a particular plane holds the lesser lives composing it under its dominion; and upon its departure the various elements, like school children released from class, return to their homes.
Theosophy requires as accurate thinking as does any science and in addition develops that which Mme. Blavatsky called the plastic power of the imagination residing in the higher mind, which sees truths as wholes. A technical study of reimbodiment in all its various aspects leads one to an understanding of the subject which might be called "three dimensional" as compared with the "flat" thinking of ordinary life.