September 19, 1907] 



NA TURE 



531 



are associated with tlie cytoplasm, as in tlie Protozoa and 

 some Coelenterates. 



Prof. J. B. Farmer, F.R.S., said that although the 

 chromosomes are probably not the actual bearers of the 

 hereditary characters, they may produce their results by 

 acting upon some specific substance in the protoplasm of 

 the cell. He pointed out that the behaviour of the chromo- 

 somes in the heterotype division, preceding the formation 

 of sexual cells, provides an arrangement for the sorting 

 out of characters such as is shown to occur by breeding 

 experiments. The chromosomes themselves consist of 

 congeries of smaller entities — the chromomeres — which are 

 probably very numerous ; possibly it is these smaller 

 entities which are associated with the hereditary 

 characters. Such an assumption would answer the often 

 raised objection that the characters exhibited by an 

 organism are more numerous than the chromosomes. In 

 any case, the heterotype division provides a mechanism 

 for arranging these entities on a mathematical basis. 

 The development of an organism on certain definite lines 

 is the result of interaction of the nucleus and cytoplasm, 

 and as there is no mechanism apparent in the cytoplasm 

 for the sorting out of characters, while such is present in 

 the nucleus, it seems reasonable to associate the latter 

 with the carrying of the hereditary characters. Moreover, 

 in many cases only the nucleus of the spermatozoon enters 

 the egg during fertilisation, and yet the parental 

 characters are conveyed. 



Mr. R. C. Punnett pointed out that in the interpreta- 

 tion of the facts of heredity the student of genetics has 

 been led to the conception of factors in the gametes upon 

 which his unit characters are based. Between the postu- 

 lated behaviour of these factors in segregation and the 

 observed behaviour of the chromosomes in the divisions 

 of the germ-cells there is a striking agreement. Never- 

 theless, certain cases of dihybridism offer phenomena 

 pointing to the existence of gametic series in which the 

 four types of gametes are produced, not in equal numbers, 

 but in such ratios as 7 : i : i : 7 or 15 : i : i : 15. If the 

 cytologist desires to regard the chromosomal elements as 

 the physical basis of heredity, he must provide some 

 scheme which will include these phenomena. 



Prof. V. H. Blackman stated his belief in the 

 chromatin as an active agent in the process of heredity. 

 Boveri's work on the multiple fertilisation of echinoderm 

 eggs seems to indicate that not only do the chromosomes 

 carry the hereditary properties, but also that they are 

 physiologically differentiated. The speaker suggested that 

 in the protozoan nucleus there is a duplication or even 

 a multiplication of the parts, and that it is not necessary 

 for the whole nucleus to divide or for chromosonies to be 

 evident ; a portion of the nuclear substance pinched off 

 may contain representatives of each of the characters. 



Mr. R. P. Gregory pointed out that in all the somatic 

 cells the division of the nucleus shows a certain form of 

 symmetry, whereas just previous to the formation of 

 gametes this symmetry is replaced by another — the hetero- 

 type division. From experiments in regeneration and 

 vegetative propagation, it appears that all the characters 

 are distributed throughout all the cells of the organism, 

 whereas breeding experiments show that segregation takes 

 place on the formation of gametes, one form of symmetry 

 being replaced by another in precisely similar manner 

 to that indicated by the study of the nucleus. It is 

 iniDossible to believe that this is a mere coincidence. 



Mr. A. D. Darbishire said he would only attempt to 

 answer one question, viz., Are there any characters which 

 depend for their manifestation on factors which exist in 

 the cytoplasm? His observations on the starch grains in 

 peas afford an affirmative answer. The difference between 

 round and wrinkled peas depends largely on the nature 

 of the starch grains. In round peas the grains are potato- 

 shaped, in wrinkled peas they are round in contour and 

 compound. In the hybrid the grain is intermediate 

 between those of the parents in three respects : — (1) in 

 contour ; (2) in compoundness, about half the grains being 

 simple and half compound : (3) in the number of pieces in 

 the compound grains, which is usually three, rarely two 

 (in non-hybrids it is six). As is well known, the form- 

 ation of starch grains depends upon certain plastids pro- 

 duced, not by the nucleus, but from others previously 

 existing in the cytoplasm. 



NO. 1977, VOL. 76"! 



Mr. L. Doncaster held that the maternal characters in 

 the hybrid larvie referred to by Prof. Hickson were only 

 found in the very early stages, and could not properly be 

 called hereditary characters. He suggested that the 

 abnormal behaviour of the nucleus in the Protozoa might 

 be associated with their great simplicity of organisation, 

 no differentiation of chromosomes bearing hereditary 

 characters having yet taken place. 



Prof. M. M. Hartog said that the essential part of the 

 chromosome in heredity appeared to be, not the chromatic 

 elements, but the achromatic basis, a view advocated also 

 by Boveri. He thought it was futile to attempt to exclude 

 tile cytoplasm from the genuine basis of heredity. With 

 reference to the suggestion, made earlier in the discussion 

 by Mr. C. C. Hurst, that cytologists should investigate 

 the relations between the nucleus and the external 

 characters of crosses. Prof. Hartog was inclined rather to 

 request breeders to investigate certain forms exhibiting 

 exceptional cell divisions. In at least two species of 

 Tradescantia single chromosomes are often left out in the 

 heterotype division of the pollen, and appear finally to be 

 digested. In several species of Hemerocallis at the same 

 stage the chromosomes are distributed into either three 

 or four cells, and the pollen grains are consequently 

 irregular in size, in number, and in the chromosomes they 

 contain. 



Prof. Hickson, in replying to the criticisms, regretted 

 that there was not time to traverse them in detail. 

 Referring to Wilson's work on the heterogeneous chromo- 

 some in the nucleus of the testis cells of Anasa frisfis, he 

 pointed out that Foote and Strobell deny the presence of 

 such a chromosome. If, as was asserted during the dis- 

 cussion, specimens of this animal from some localities 

 possess this chromosome while others from a different 

 localitv do not, that is a strong argument against the all- 

 powerful influence of the chromosomes in regard to the 

 hereditary characters. 



The Experimental Study of Heredity. 

 Mr. R. C. Punnett illustrated his lecture on this sub- 

 ject by a series of actual examples, drawn chiefly from 

 fowls and sweet-peas. He pointed out that the laws of 

 heredity associated with the name of Mendel apply equally 

 to plants and animals; the comb of the fowl, the stature 

 of the sweet-pea, the colour of the stock, the hair of 

 the rabbit, rust immunity in wheat, and some diseases in 

 man, all conform to the same laws of heredity. Experi- 

 mental work with animals may well lead to a solution 

 of many problems in human disease ; but, important as are 

 the practical results, this study has a still greater import- 

 ance in relation to our scientific conceptions, for it must 

 radically affect our views of the process of evolution, the 

 nature of mutation, and the physical basis of heredity. 



Protosoa. 



Mr. F. B. Rowley exhibited a series of models of 

 Protozoa — Amoeba, Vorticella, Parameeciuni, Actino- 

 sph.-erium, and the parasite of human malaria in blood 

 corpuscles — constructed chiefly of gelatin, which give an 

 exce)\ent idea of the appearance of these organisms in 

 life. 



Mr. H. B. Fantham discussed the classification of the 

 Haplosporidia. He and Dr. Ridewood suggest the division 

 of the group into two sections : — 



(i) Polysporulea, in which the pansporoblast gives rise 

 to nine or more spores, e.g. Rhinosporidium, Neuro- 

 sporidium. 



(2) Oligosporulea, in which the pansporoblast gives rise- 

 to a few (four) spores or to a single spore, e.g. Haplo- 

 sporidium, Bertramia, Coelosporidium. 



The Movements of Spirochaetes, 

 Mr. Fantham pointed out that the nature of the move- 

 ments of Spirochetes would serve as an aid in separating 

 this genus from Spirillum. Knowledge of these move- 

 ments would therefore be of value in connection with the 

 vexed question of the nature of the organism of relapsing 

 fever. Spirochaetes, especially S. anodoutae, with its 

 pointed ends, usually move very rapidly, but in slowly 

 moving specimens the organism can be seen to move for- 

 ward while turning on its long axis. The motion can be 



