September 27, 1906J 



NA TURE 



551 



than the others in two species of GIraucIia. Lavigeria, the 

 only genus of which a female has been examined, is vivi- 

 parous, and its radula most closely resembles that of the 

 Melaniid genus Chiara, while the radula of Giraudia is 

 clearly similar to that of the Melaniid genus Ancylotus. 



Dr. G. A. Boulcngcr, in reviewing the evidence afforded 

 by a study of the fishes, said that the Cichlid fishes, which 

 form so large a proportion of the fishes of Tanganyika, 

 are examples of an extraordinary modification of one type 

 which has entered fresh water all over Africa, and that 

 this lake seems to have served as a nursery for genera and 

 species of this family. The Cichlids of Victoria Nyanza 

 seem to have aris(>n, like those of Tanganyika, from a 

 small number of generalised types. The fishes of Tangan- 

 yika indicate a long isolation of the lake, perhaps extending 

 back to Miocene times. 



The Nature of Fertilisation. 



I he discussion (conjointly with Section K) on the nature 

 • if fertilisation was initiated by Dr. V. H. Blackman, who 

 i;ive a brief account of the recent work on which the 

 present views of fertilisation are based, dealing specially 

 with the rile of the chromosomes, and taking as a starting 

 puint the theory put forward by Montgomery (1901), that 

 in synapsis the maternal and paternal chromosomes unite 

 ill pairs and are later separated by the reduction division, 

 which thus divides the somatic chromosomes into two 

 groups. Fertilisation appears to be incapable of exact de- 

 finition, for apogamy and parthenogenesis link it on to 

 vegetative reproduction, and, indeed, nuclear fusions and 

 reductions occur in plants apart from reproduction, e.g. in 

 graft hybrids of Mespilus and Crataegus there is evidence 

 that the fusing of vegetative cells has led to the mixing 

 of characters. 



Prof. Calkins described his experiments proving that it 

 was possible to carry cultures of Paramoecium through a 

 certain number of periods of depression, and to renew their 

 vitality by means other than nuclear fusion (conjugation), 

 he having been able to do this by treatment with beef 

 extract and with extract of pancreas and brain. Prof. M. 

 Hartog cited what he considered to be comparable cases 

 of the orange, Funkia, &c., where cells of the nucellar 

 tissue grow into the embryo-sac cavity, and, under the 

 stimulus of the exceptional nutrition, grow into embryos 

 which behave exactly like the normal embryos produced by 

 the fertilised oosphere in the same favoured feeding place. 



Mr. L. Doncaster gave a brief account of the maturation 

 of parthenogenetic eggs, pointing out that many eggs which 

 produce, not only one, but two polar bodies, may develop 

 parthenogenetically. The fate of the polar nuclei varies 

 considerably ; in some cases they are cast out and lost, in 

 others they remain in the egg, and (as in Artemia) one 

 may conjugate with the egg nucleus, taking the place of 

 the spermatozoon. 



Dr. Rosenberg (Stockholm) described his experiments on 

 the production of hybrids of Drosera rotundifolia and 

 D. longifolia, the cells of the former having ten and of 

 the latter twenty chromosomes. In certain of the daughter 

 nuclei, ten, eleven, or twelve chromosomes move to one 

 pole during division, the same number to the other pole, 

 and between these lie a number of separate chromosomes, 

 which are later taken into one or other of the division I 

 nuclei. In Hieracium, one polar nucleus returns to the 

 embryo-sac cell and fuses virith the egg-cell, producing a 

 cell with unreduced number of chromosomes. Dr. Ostenfeld ' 

 afterwards stated that Hieracium was able to produce 

 fruits without ordinary fertilisation having taken place. I 



Prof. Hickson considered that the evidence that the 

 chromosomes are the sole bearers of the hereditary 

 characters had been much weakened during recent years 

 by the results of such experiments as those on enucleated 

 eggs fertilised by the sperms of another species, which gave 

 rise to larvae showing sometimes paternal and sometimes 

 maternal and mixed characters. 



Mr. H. Wager pointed out that in many of the lower 

 organisms the nucleus does not seem to be concerned, as 

 in higher organisms, in the blending, during fertilisation, 

 of two distil. ct lines of descent, but presides over the 

 nutritional activities of the cell, and fertilisation is replaced 

 hr various nutritional devices. I 



Spicule Formation in Sponges. 



Prof. Minchin discussed a number of facts bearing on 

 spicule formation in calcareous sponges, and concluded that 

 the form of primary spicules is in no way dependent upon 

 the physical properties of the material (calcite), but is 

 regulated solely by biological conditions. When, however, 

 primary spicules are joined together to form spicular 

 systems, the physical properties of the material may exert 

 an influence upon the form of the spicule as a whole by 

 determining the angles at which the rays join together. 

 Prof. Dendy dealt more particularly with the evolution of 

 the various forms of siliceous spicules in the Tetra.xonid 

 sponges, showing that they are all derivable from a primi- 

 tive tetraxon form. He showed that these spicules origin- 

 ated singly in mother-cells, and endeavoured to explain 

 their great diversity of form as the result of the action of 

 variation, heredity, and natural selection. Mr. W. Wood- 

 land contended that the forms of spicules are not inherited, 

 for such an inheritance of forms of spicules adapted to the 

 architecture of the organism implies that wandering cells 

 (scleroblasts) are severally able to produce a part of the 

 adult organism, an organ, in fact, related in form to the 

 other parts. The collection of scleroblasts disposed about 

 the spicule forming the protoplasmic mould in which the 

 spicule is deposited is the organ assumed to be inherited. 

 Such a theory seems to be contradicted by the facts of 

 experimental embryology, which shows that a blastomere 

 can only give rise to an integral part of the adult organism 

 in virtue of its localised connection with other blastomeres. 

 Mr. Woodland concluded, therefore, that the form of the 

 deposited spicule determines the disposition of the sclero- 

 blasts, and not vice versa (as held by the advocates of the 

 inheritance of spicule form), and that spicular phenomena 

 may be fully explained by reference to known physical facts. 

 He suggested that many spicules are probably closely allied 

 in their mode of origin to the curious structures (colloido- 

 morphs) formed by mineral substances deposited in colloidal 

 media. 



Fishery Problems and Marine Investigations. 



Dr. E. J. Allen opened a discussion on the relations of 

 scientific marine investigations to practical fishery problems. 

 He pointed out that the great growth of the fishing in- 

 dustry during the last thirty years has been accomplished 

 by practical fishermen, and, in some directions at least, 

 science could even now help little, e.g. in the case of drift- 

 net fisheries any attempt to increase the supply would 

 probably be futile. In the case of trawl fisheries a diminu- 

 tion in the source of supply has taken place, but there is 

 hope of increasing the actual supply of fish in the grounds 

 by (i) regulation and restriction of fishing; (2) re-stocking 

 exhausted grounds by hatching or by transplantation ; and 

 (3) destruction of the enemies of food fishes. Before such 

 measures can be carried out with much hope of success, a 

 complete and exact knowledge is necessary of the habits 

 and life-histories of the fishes, and of the conditions under 

 which they live. 



Dr. W. Garstang discussed the question of the diminution 

 of the stock of plaice in the North Sea, and the methods 

 suggested for increasing the supply. The diminution is 

 supposed to be caused by the excessive fishing of young fish. 

 In the southern part of the North Sea (Flemish Bight) 

 most of the fish caught are less than 30 cm. in length, 

 while on the Dogger Bank most are more than 30 cm. 

 long. From January to June the small plaice are found 

 chiefly inshore and out to the ii-fathom line; from June 

 to December they travel out to the 20-fathom line. This 

 gives a rough idea of the migration of the young plaice 

 outward into deeper water during the summer and autumn 

 months, and is confirmed by the results of marking experi- 

 ments. The migration of fish to the Dogger Bank is, there- 

 fore, not a direct and simple one, but takes place in at 

 least two stages. Much more information is still required 

 concerning the normal distribution of fishes of various sizes, 

 the migration of young fish, and the causes which deter- 

 mine rapidity of growth. 



Mr. G. L. Alward expressed his belief in the value of 

 fish hatcheries, and also advocated the exploration of the 

 area between Norway and Iceland in the hope that new 

 fishing ground mav be found so as to relieve the present 



NO. 1925, VOL. 74.] 



