July 13, 1876] 



NA TURE 



235 



acting pump (Fig. 8) ; these are classed together, and a 

 closer examination of the function and elements of each 

 will immediately show the correctness of so doing. The 

 twobarsrandf in the ratchet train correspond with the two 

 pump rods and buckets. The pumpbarrels ^^^ correspond 

 with the guide frames d d ol the ratchet train, the valves 

 b and b correspond with the pawls b and b, while the water 

 in the two barrels is the exact equivalent of the ratchet 

 a a. As the bar c descends the pawl b would pass over 

 a certain number of teeth of the ratchet equal to the 

 number in the length of stroke of r, if the bar c was dis- 

 connected with the lever but as it is, during the descent 

 of c, through a certain distance the ratchet is lifted an 

 equal distance by the other pawl bj thus we see that each 

 pawl passes over twice as many teeth of the ratchet as 

 correspond to the length of its stroke. This has an exact 

 parallel in the double-acting pump, for there also each 

 bucket in its down stroke moves through a length of 

 water equal to double the length of its stroke. The fol- 

 lowing is the outline of Prof. Reuleaux' Classification of 

 Constructive Elements : — 

 Rigid Elements — 



Joints (for forming links) such as rivets, keys, keyed 

 joints. 



Elements in pairs or in links, such as shafts and 

 axles, levers, cranks, &c. 

 Flectional Elements — 



Tension organs by themselves and used with chain- 

 closure, such as belts, cords. 



Partners of pressure organs such as pistons and 

 plungers, steam cylinders and pump barrels. 



Springs. 

 Trains — 



Click-gear. 



Brakes. 



Movable couplings and clutches. 

 In conclusion we must say that the cuts illustrating the 

 book, are much superior to those generally to be found in 

 theoretical books on machinery, but they do not, of course, 

 equal the elaborate working drawings to be found in certain 

 books on machine design. In Fig. 169^ p. 218, the rope ap- 

 pears to have somewhat lost its way. The translator has 

 done his work most admirably, and great must have been 

 the ingenuity required to manufacture some of the names 

 here presented for the first time to the English reader. 

 In fact we could hardly imagine a book more difficult to 

 translate, on account of the great number of specially- 

 constructed words in it, nor do we rertfember havmg read 

 one in which the duties of the translator have been more 

 successfully carried out. The book appears at a par- 

 ticularly suitable time, now that the beautiful and exten- 

 sive collection of kinematic models by Prof. Reuleaux, 

 designed by him and constructed especially to illustrate 

 his treatment of the theory of mechanism, is to be seen 

 at the Loan Collection of Scientific Instruments at South 

 Kensington. 



PERIGENESTS v. PANGENESIS— HAECKEUS 



NEW THEORY OF HEREDITY 

 T T NDER the title " Perigenesis der Plastidule oder die 

 ^ Wellenzeugung der Lebenstheilchen," Prof. Haeckel 

 has published quite recently a pamphlet containing an 

 attempt to furnish a mechanical explanation of the ele- 

 mentary phenomena of reproduction which shall be more 

 satisfactory than Mr. Darwin's ingenious and well-known 

 theory of Pangenesis. I shall endeavour to show that 

 Prof. Haeckel's theory is essentially that with which both 

 English and German students of Mr. Herbert Spencer's 

 works have long been familiar ; and that it does not fur- 

 nish a clearer explanation than does Mr. Darwin's Pan- 

 genesis, of the special facts of heredity which Mr. Darwin 

 had in view. 



Haeckel commences with a very concise statement 

 of what is at present known as to the visible compo- 

 sition of " plastids," those corpuscles of life-stuff called 

 "cells" by Schleiden and Schwann, " elementary organ- 

 isms" by Briicke, "life-units" by Darwin. Most plas- 

 tids possess a differentiated central kernel or nucleus, 

 which again possesses one or more nucleoli. The sub- 

 stance of which the body of such a nucleated plastid or 

 true cell is mainly composed is generally known by von 

 Mohl's term, " pro oplasma." Haeckel proposes to dis- 

 tinguish the substance of the nucleus by the name 

 " coccoplasma." In the simplest form of plastid, the 

 " cytod," which is devoid of nucleus, and is exhibited by 

 those lowly organisms known as Monera, by the young 

 Gregarina (Ed. van Beneden), by the hyphae of some 

 Fungi, and by the ripe egg of all organisms (if we may 

 judge from the results of the most recent researches), 

 coccoplasm and protoplasm are not differentiated, but 

 exist as one substance, which Haeckel, following Ed. van 

 Beneden, distinguishes as " plasson." Whether these 

 distinctions have a real value or not, is of no moment 

 for the question in hand. It is a widely-accepted doc- 

 trine — in fact, the fundamental generalisation on which 

 Biology as a science rests — that the excessively complex 

 chemical compound which forms the substance of plastids 

 or life-units is the ultimate seat of those phenomena or 

 manifestations of energy which distinguish living from 

 lifeless things — to wit, growth by intus-susception, repro- 

 duction, adaptation, and continuity or hereditary trans- 

 mission. Leaving Prof Haeckel's pamphlet for a time, 

 let us go back thirteen years. 



As long ago as July, 1863, Mr. Herbert Spencer, in his 

 " Principles of Biology," pointed out at considerable 

 length (vol. i., p. 181) that the assumption of definite 

 forms, and the power of repair exhibited by organisms, 

 is only to be brought into relation with other facts (th it 

 is to say, so far explained) by the assumption that certain 

 units composing the living substance or protoplasm of 

 cells possess " polarity" similar to, but not identical with, 

 that of the units whijh build up crystals. Mr. Spencer 

 is careful to explain that by the term " polarity " we mean 

 simply to avoid a circuitous expression, namely, the still 

 unexplained power which these units have of arranging 

 themselves into a special form. He then points out that the 

 units in question cannot be the molecules of the proximate 

 chemical compounds which we obtain from protoplasm — 

 such as albumen, or fibrin, or gelatin, or even protein. 

 Further he shows that they cannot be the cells or mor- 

 phological units, since such organisms as the Rhizopods 

 are not built up of cells, and since, moreover, "the forma- 

 tion of a cell is to some extent a manifestation of the 

 peculiar power " under consideration. "If then," he con- 

 tinues, " this organic polarity can be possessed neither 

 by the chemical units, nor the morphological units, we 

 must conceive it as possessed by certain intermediate 

 units, which we may term physiological. There seems 

 no alternative but to suppose that the chemical units 

 combine into units immensely more complex than them- 

 selves, complex as they are ; and that in each organism, 

 the physiological units produced by this further com- 

 pounding of highly compound atoms, have a more or less 

 distinctive character. We must conclude that in each 

 case, some slight difference of compcsition in these units, 

 leading to some slight difference in their mutual play of 

 forces, produces a difference in the form which the aggre- 

 gate of them assumes." 



Further on Mr. Spencer applies the hypothesis of 

 physiological units to the explanation of the phenomena 

 of heredity, introducing the subject by the following 

 admirable remarks, which appear to me to assign in the 

 most judicious manner, their true value to such hypo- 

 theses and to be as strictly applicable to later specula- 

 tions as to his own. " A positive explanation of heredity 

 is not to be expected in the present state of biology. We 



