28 SUMMARY OF CURRENT RESEARCHES RELATING TO 
of forces wholly predetermined by the constitution of the ovum, Minot 
maintains that the formative forces are distributed through all the parts. 
The evidence for this is found in the facts of regeneration, in the occa- 
sional doubling of parts, and in the phenomena of asexual reproduction, 
wherein it appears that each part shares in the essence of the organism, 
is a sample or model of it, and tends partially or perfectly to reproduce it. 
The death of Protozoa is not homologous with the death of Metazoa ; 
death for a Protozoon means the destruction of a cell, for a Metazoon the 
breaking up of an alliance, when in the course of cell-generations some 
which are essential grow old or weak or go out of gear. Weismann 
has not disproved the occurrence of senescence in Protozoa. “ He misses 
the real problem.” 
Larvae, living freely, are more primitive than embryos which are 
nourished by yolk within the egg. All the lower animals have only 
larvae, and yolk appears and increases very gradually in the animal 
series. But larvae show no special cells which keep up the continuity 
of germinal stuff; they are thoroughly differentiated.. Indeed, germ- 
plasm in Weismann’s sense does not exist. The development of an 
organism depends not upon material contained in special cells, but on a 
particular state or stage of the organisation. In short, all cells are 
potentially reproductive or morphogenetic, and may become really so in 
various conditions, of which the fertilisation of the ovum is only one. 
The great difference between embryo and larva lies in the fact that 
the former have a longer period for the multiplication of indifferent 
cells — an adaptation securing progress in organisation. 
Rejuvenescence is one of the chief vital phenomena. The rejuvenated 
state of a cell is marked by the preponderance of nucleus over cytoplasm, 
by the undifferentiated state of the latter, and by the capacity for rapid 
multiplication. Somatic cells are those in which the activity of heredity 
is inhibited by senescence or differentiation, but in certain conditions 
they may be rejuvenated, and show more or less reproductive power. 
In the origin of a new part there are two stages — the formation of 
the rudiment, and its differentiation. The undifferentiated state is not 
useful ; it occurs in virtue of a post-selection or Nachauslese , which 
affects the result, just as natural selection affects not the mother wasp 
which lays its eggs in a leaf, but the larva which is hatched there. 
Minot, as he said in 1893, regards the recapitulation theory as 
scarcely half true, wherein he agrees with Sedgwick. He asks how 
characters disappear ; to say “ by disuse ” is no explanation, and “ pan- 
mixia ” is an hypothesis founded on nothing. The loss of ancestral 
characters in an embryo is brought about by post-selection, the cells 
remaining in the young or rejuvenated state, so that they subsequently 
bring about a new differentiation. 
Minot regards Weismann’s theory as mystical, without basis of fact, 
illogical, misleading, and unscientific. It would be interesting to know 
what Weismann thinks of Minot’s. 
Formative Stimuli in Development.* — Herr Curt Herbst has 
already shown at length that “directive stimuli” play an important 
part in developmental processes ; he now proceeds to discuss formative 
* Biol. Centralbl., xv. (1895) pp. 721-15, 753-72, 792-805. 
