By Dr. R. VON LENDENFELD.

[The following article appeared originally, last year, in the German scientific monthly, Humboldt. It, is reproduced here (by permission) - the English from the hand of Mr. A.E. Shipley - as a specimen of the kind of general speculation to which modern biology is giving rise. - EDITOR.]

To Weismann is due the credit of transforming those vague ideas on the immortality of the germ plasma which have been for some time in the minds of many scientific men, myself among the number, into a clear and sharply-defined theory, against the accuracy of which no doubt can be raised either from the theoretical or from the empirical standpoint. This theory, defined as it is by Weismann, has but recently come before us, and some time must elapse before all the consequences which it entails will be evident. But there is one direction which I have for some time followed, and indeed began to think out long before Weismann's remarkable work showed the importance of this matter. I mean the origin of the conception of the immortal soul.

Before I approach the solution of this problem, it may be advisable to recall in a few words to my readers the theory of the immortality of the germ plasm.

All unicellular beings, such as the protozoa and the simpler algae, fungi, etc., reproduce themselves by means of simple fission. The mother organism may split into two similar halves, as the amoeba does, or, as is more common in the lowest unicellular plants, it may divide into a great number of small spores. In these processes it often happens that the whole body of the mother, the entire cell, may resolve itself into two or more children; at times, however, a small portion of the mother cell remains unused. This remnant, in the spore-forming unicellular plants represented by the cell wall, is then naturally dead.

From this it follows that these unicellular beings are immortal. The mother cell divides, the daughter cells resulting from the first division repeat the process, the third generation does the same, and so on. At each division the mother cell renews its youth and multiplies, without ever dying.

External circumstances can, of course, at any moment bring about the death of these unicellular organisms, and in reality almost every series of beings which originate from one another in this way is interrupted by death. Some, however, persist. From the first appearance of living organisms on our planet till to-day, several such series - at the very least certainly one - have persisted.

The immortality of unicellular beings is not at any time absolute, but only potential. Weismann has recently directed attention to this point. External occurrences may at any moment cause the death of an individual, and in this way interrupt the immortal series; but in the intimate organization of the living plasma there exist no seeds of death. The plasma is itself immortal and will in fact live forever, provided only external circumstances are favorable.

Death is always said to be inherent in the nature of protoplasm. This is not so. The plasm, as such, is immortal.

But a further complication of great importance affects the reproduction and the rejuvenescence of these unicellular organisms; this is the process of conjugation. Two separate cells, distinct individuals, fuse together. Their protoplasmic bodies not only unite but intermingle, and their nuclei do likewise; from two individuals one results. A single cell is thus produced, and this divides. As a rule this cell seems stronger than the single individual before the union. The offspring of a double individual, originated in this way, increase for some time parthenogenetically by simple fission without conjugation, until at length a second conjugation takes place among them. I cannot consider further the origin of this universally important process of conjugation. I will only suggest that a kind of conjugation may have existed from the very beginning and may have been determined by the original method of reproduction, if such existed.

At any rate conjugation has been observed in very many plants and animals, and is possibly universally present in the living world.

Conjugation does not affect the theory of immortality. The double individual produced from the fusion of two individuals, which divides and lives on in its descendants, contains the substance of both. The conjugating cells have in no way died during the process of conjugation; they have only united.

If we examine a little more closely the history of such a "family" of unicellular beings from one period of conjugation to the next, we see that a great number of single individuals, that is, single cells, have proceeded from the double individual formed by conjugation. These may all continue to increase by splitting in two, and then the family tree is composed of dichotomously branching lines; or they may resolve themselves into numerous spores, and then the family tree exhibits a number of branches springing from the same point.

The majority of these branches end blindly with the death, caused by external circumstances, of that individual which corresponds with the branch. Only a few persist till the next period of conjugation, and then unite with other individuals and afford the opportunity for giving rise to a new family tree.

All the single individuals of such a genealogical table belong to one another, even though they be isolated. Among certain infusoria and other protista, they do, in fact, remain together and build up branching colonies. At the end of each branch is situated an infusorian (vorticella), and the whole colony represents in itself the genealogical family tree.

In the beginning, there existed no other animal organisms than these aggregations of similar unicellular beings, all of which reproduced themselves. Later on, division of labor made its appearance among the individuals of the animal colony, and it increased their dependence upon one another, so that their individuality was to a great extent lost, and they were no longer able to live independently of one another.