196 
SCIENCE. 
TRANSFORMATION OF PLANORBIS. 
A PRACTICAL ILLUSTRATON OF THE EVOLUTION OF SPECIES. 
By Prof. Alpheus Hyatt. 
II. 
Bui we see that both the favored and unfavored found 
their appropriate spheres, and that even the deformities 
were perpetuated, and became distinctive of species. 
Another characteristic which does not come under the 
dominion of any law of natural selection is the inevitable 
tendency to form an asymmetrical spiral in all the later oc- 
curring members of each series, whether progressive or re- 
trogressive. 
The lecturer then explained, by the aid of diagrams and 
a model, that the forms of shells are due to the successive 
imbricated layers built up by the border of the mantle in 
all mollusks. Secondly, that any force tending to com- 
press one part of the secreting border more than another 
would occasion a narrowing of the imbricated layers of 
that part, and cause a twist or spiral to be formed. Thirdly, 
that the aspect of all the spirals examined shows that the 
shells are acted upon by such a force — gravitation, and in 
no other way can we account for their shape, and the ob- 
vious direction in which the compression of the border 
takes place. 
The mathematical regularity of the spirals is explained 
if we admit the constant action of a universally distributed 
physical force upon the building up of the shell. 
Diseased and outgrown, or old shells, were shown in order 
to enforce the fact that when an animal becomes weakened 
the shell shows its effect by the irregularities of the spiral. 
The excessively irregular forms of the oyster show that 
when the action of gravitation is in part eliminated the 
asymmetry is proportionately greater or less, and also that 
distortions occur in the internal soft body, as in the gills, 
and in the distribution and structure of the blood-vessels 
and mantle, which are quite different on the lower side 
of the adult oyster and upon the upper. 
The oyster and all lamellibranchs grow not in the direction 
of effort, but in that of least resistance. The clam and the 
mussel were adduced to show this as well as the oyster. 
The forms of these shells are bilateral, but their anterior 
ends are compressed more than their posterior portions, 
therefore the valves grow faster towards the posterior than 
towards the anterior ends. Sooner or later when any soft- 
bodied animal lies habitually on its side, the originally bi- 
lateral or spherical form of the tree animal must become 
distorted, as is the case with all attached animals, like the 
attached forms of protozoa, sponges, coelenterata, echino- 
dermata, and so on. It is not difficult to show that their 
spiral, spherical, or bilateral symmetry is proportional, in 
all cases known to the speaker, to the amount of freedom 
in the growth of the parts ; the freer the part the more sym- 
metrical, the more attached or supported the more asym- 
metrical. Examples of shells like those of Magilus anti- 
qtius were cited in support of this view. 
The attraction of gravitation is eliminated during the 
growth of this shell, by the coral which surrounds it ; and 
the result, as also in the cases of many of the Vermetidae, 
which receive a similar perfect support, is the formation of 
a wholly irregular tube, though the young are, while still 
free, provided with the ordinary turreted shell. 
To show that the bilaterality of soft parts was produced 
by the attraction of gravitation on a soft growing body, the 
lecturer described several illustrations, especially the case 
of the Eolidae, which have a coiled shell in the young, but 
lose this and become, during growth, perfectly symmetrical 
and soft-bodied. He also showed, that in no other way can 
we account for the extraordinary mixture of asymmetry in 
the shells and symmetry in the softer, free moving parts of 
the same animal among the Gasteropoda and other animals. 
The effects of heredity were also discussed, and it was 
shown that when a symmety, as distortion, was introduced, it 
occurred usually on the outer whorl, or during the latter 
stages of the growth, and that as time went on, this same 
characteristic appeared at earlier and earlier stages in the 
growth of successive descendants. The final effect of this 
law is the entire replacement of older ancestral characteris- 
tics by those which are newly introduced. 
Thus the turreted asymmetrical spiral is found, as in the 
Steinheim shells, to gradually replace the more nearly sym- 
metrical form of the immediate ancestors and the absolutely 
symmetrical form of the disc or shell, ovishell, as it is 
called, in all species. It was claimed that this law of here- 
dity was absolute and independent, as one of the results of 
growth ; and, that neither the variations, such as the forma- 
tion of the asymmetrical spiral, nor its perpetuation and 
increase in successive generations of forms could be attrib- 
uted to any law of natural selection. 
The lecturer then, however, proceeded to show that the 
differences between the different series of shells could only 
be accounted for on the supposition of advantage and dis- 
advantage, and took the ground that the Darwinian hypo- 
thesis applied perfectly to the explanation of the survival 
of only four distinct varieties out of the many which emi- 
grated into the Steinheim basin, and tried to prove this by 
numerous instances quoted from Verrill and other authori- 
ties, showing that uniform physical causes must have a 
certain uniformity of result, which was not the case with the 
differences of the different series. 
When, however, the action of natural selection had main- 
tained the new differences for a certain length of time, until 
they had begun to be inherited, he claimed that it ceased to 
have any farther effect upon the organization. 
Wherever the species might be found or whatever the 
surroundings there would be one thing absolutely certain ; 
the forms during their growth would repeat the selected 
differences during their early stages of growth. In other 
words, the characteristics originally established by reason 
of their advantage or disadvantage in the battle of life, as 
soon as they become fixed in the organization, are no longer 
under the control of natural selection, which must vary 
with the immediate surroundings, but under that of heredity 
by acceleration. 
The conclusions, besides those given in your report, were 
as follows : 
“At thebaseof this conception of an animal lies growth.” 
Arising by growth through processes, which have been 
extensively studied, are, the bud, the egg, and all the 
phenomena connecting animals and plants according to the 
laws of heredity. 
The action of growth and heredity, under the constant con- 
trol of physical forces * gives the forms and many of the char- 
acteristics which distinguish a form from its immediate 
parents or ancestors, or from the forms occurring in othei 
localities ; in other words, the variations. The mutual ac- 
tion and re-action of animals and plants upon one another 
according to the laws of natural and sexual selection, etc., 
give it fixity in the organization to certain of these varia- 
tions. 
* Of course, in this view, the physical force is the immediate cause of 
every condition of symmetry of form, as well as of every variation not de- 
rived from inheritance. The animal, in other words, is looked upon as a 
plastic, growing organism, acted upon from outside by physical forces, 
which modify it perpetually, and upon which it re-acts by means of its 
powers of growth and heredity. The former tend to cause perpetual vari- 
ation, the latter to preserve the type by renewing — “rejuvenating” it 
perpetually in each successive generation. 
We cannot account for the suitability of organisms, and their adapta- 
tions to every situation in time, as the distribution on the existing surface 
of the earth, or for the results of experimental zoology, without acknow- 
ledging the paramount influence of physical forces. 
Nor can we, on the other hand, account for the comparative invariabil- 
ity of the embryo for indefinite periods of past time, or for the preser- 
vation of the type in spite of the perpetual changes introduced by 
physical changes on the earth’s surface, unless due w'eight be given to 
the reaction of the growth forces and heredity by acceleration, which 
tend to preserve original types comparatively unchanged. 
An organism is not entirely at the mercy of the elements, but poss-sses 
a power which, within a certain sphere, acts not only for the preservation 
of its life, but also for the preservation of its own characteristics, and, 
through heredity, causes the perpetual recurrence of similar characteris- 
tics and similar changes, what are usually called parallelisms, in successive 
generations of genetically connected individuals, forms a species wherever 
they occur in time, and under whatever circumstances of local distri- 
bution upon the surface of the earth. 
Manufacture of Factitious Butter in thr United 
States. — A compilation from American and English sources 
shows that factitious butter contains only 1.823 P er cent, of 
butyrine, caprine, caproine, and capryline, as against 7.432 
per cent, in the natural product. — Moniteur Scientifique. 
