196 



SCIENCE. 



TRANSFORMATION OF PLANORB1S. 



a practical illustraton of the evolution of species. 



By Prof. Alpheus Hyatt. 



II. 



But 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 iree 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- 

 quus 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 Vermctidae, 

 which receive a similar perfect support, is the formation of 

 ;i wholly irregular tube, though the young are, while still 

 free, provided with the ordinary turreted shell. 



'J'o 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 Kolidvc, which have a coiled shell in the young, hut 

 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, 11 

 occurred usually on the outer whorl, 01 during the latter 



Stages of the growth, and that as time went on, this same 



characteristic appeared at earliei and earliei stages in the 



growth of successive descendants. flu final effect of this 

 law is the entire replacement of older ancestral ehaiaetei is- 



1 1 < s by those whi« li 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 the base of 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 ils 

 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 weight 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 possrsscs 

 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 ok 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 



but] tine, caprine, caproine, and capryline, as against 7.432 



, per cent, in the natural product. — Moniteur Scic>iti/i</nr. 



