HA RD WICKE'S SCIENCE- G OSSIP. 



247 



to their embryonic states. Professor Balfour* con- 

 sidered that " the function of forming polar cells 

 has been acquired by the ovum for the express 

 purpose of preventing parthenogenesis ; " but the 

 fact that Weismann t has observed the extrusion of 

 polar bodies in parthenogenetic crustaceans, while no 

 extrusion of polar bodies has been found to obtain 

 in the rotifera and arthropoda, somewhat negatives 

 this explanation. CamoyJ is strongly opposed to 

 this view. He will not admit that the extrusion of 

 the polar bodies equals the extrusion of the male 

 idioplasm from the ovum, so that what is left is 

 entirely female, and that the extrusion of the seminal 

 globule equals the extrusion of the female idioplasm, 

 so that what is left in the spermatozoon is entirely 

 male. But other authors are not so entirely opposed 

 to this view as is Carnoy. Dr. McKendrick § says 

 that, even if the observation of Weismann be correct, 

 it does not seem to him " to destroy the validity of 

 Balfour's theory, but only to show that it is less 

 extensive in its application. The extrusion of polar 

 bodies by parthenogenetic ova may be the survival of 

 an ancestral habit, and possibly after removal of the 

 polar body there may still be enough of the male 

 matter left to allow of development going on without 

 the entrance of a fresh spermatozoid." 



That, however, Balfour's theory must be modified 

 to some extent admits of no doubt, since the male 

 idioplasm cannot be regarded as entirely male, nor 

 the female idioplasm as entirely female, since — as has 

 been pointed out by KoUiker and Strasburger — the 

 male parent may send onward traits of the paternal 

 grandmother and great-grandmother, and the female 

 parent may send on traits of the maternal grandfather 

 and great-grandfather, besides peculiarities which 

 belong strictly to themselves alone. Hence, we may 

 concede, may arise atavism. The greater the differ- 

 ence between the idioplasms of the two individuals 

 engaged in coitus, the greater will be the stimulus 

 setting into action the division of the oosperm and the 

 development of a new individual. Self-impregnation 

 has been observed in Limncca auricularia by von Baer 

 and in some species of Planorbis ; but it is hard to con- 

 sider for one moment that the ova would be fertile, since 

 the spermatozoa fecundating them came from exactly 

 the same kind of germinal elements in one and the 

 very same organ, and hence the male and the female 

 idioplasms were theoretically equal one to the other, 

 and no stimulus consequently would be set up by 

 their union to give rise to continuous segmentation 

 of the oosperm. The difficulty about these two 

 theories — those of Strasburger and Naegeli — is to 

 account for the manner in which the somatic idio- 

 plasm becomes converted into germ idioplasm, and 



• " Comparative Embryology," vol. i. p. 72. 



+ " Richtungsk6rper bei parthenogenetischen Eiem," Zool. 

 Anz., Sept. 27, ib86. 



X " La Cytodi^rese de Tceuf." La Cellule, torn. iii. fasc. x, 

 p. 60. 



} -"Text-book of Physiology," footnote, p. 238. 



hence Weismann* has brought forward a theory which 

 he calls " the continuity of the germ-plasma." He 

 believes that what is transmitted is neither idioplasm 

 nor nucleohyaloplasm, but that it is a substance of 

 peculiar molecular structure resident in the nucleus, 

 to which he has given the name of keimplasma ; that 

 this keimplasma is not produced from somatic-plasma, 

 but is independent of it ; that it does not alter in its 

 characters from one generation to another. He con- 

 siders also that this keimplasma derived from the 

 parents is not entirely used up in the development of 

 the embryo, and that the residuum is applied to the 

 production of the keimplasma of the succeeding 

 generation. He explains away the transmission of 

 hereditary qualities by considering that it is due to an 

 exceedingly strong influence of the germ-plasma upon 

 the development of somatic-plasma in the embryo. 

 These are the main features of Weismann's theory. 

 But, as pointed out by McKendrick {loc. cit.), while 

 on the one hand it may remove some of the difficulties, 

 yet, on the other hand, the acts of hereditary trans- 

 mission remain unexplained. For, " if the portion of 

 germ-plasma not laid aside influences the develop- 

 ment of the body, conferring on each tissue and organ 

 at least some of the pecuUarities of the parent, how 

 does it so ? The molecular mechanism by which this 

 is accomplished is inexplicable. On the other hand, 

 if this germ-plasma does not so influence development, 

 how are the facts of hereditary transmission to be 

 explained ? " In a recent pamphlet f Prof. Nussbaum, 

 with much forceful argument, ascribes variation to 

 the action of extrinsic and intrinsic forces upon one 

 another. " Selection is a consequence of this inter- 

 action, since it always rests with the numerical strength 

 of the forces, whether the individuals and their germi- 

 nal material persist, change, or perish." Thus much 

 for the most principal theories of heredity. I have by 

 no means exhausted the subject, but I hope that I 

 have shown the conchologist % that the cause of varia- 

 tion will be no sooner brought to light by the getting 

 together of varietal collections from different localities, 

 and by the wholesale naming of varieties as a help 

 thereto. I hope I have shown him that, if the cause 

 of variation is to be sought anywhere, it is to be sought 

 in the plastic nature of the protoplasm of the ovum and 

 of the spermatozoon. In his untiring zeal to seek the 

 cause of variation by handling and pondering over the 

 shells in his cabinet, he has forgotten a dictum of one 

 of the oldest conchologists, Adanson, who, in his 

 " Voyage to Senegal," which was published in the 

 year 1757, stated that, to get a true knowledge of the 

 moUusca, it was necessary to know the anatomy 



• " Die Continuitat des Keimplasma's als Grundlage einer 

 Theorie der Vererbung," Jena, 1885. See also Proie^sor 

 Moseley in " Nature," vol. xxxiii. p. 154. 



t " Ueber Vererbung," 1888. 



j This -WQTd, though sanctioned by usage, I may pjint out, 

 is not quite correct. It should be conchy liologist ; concliuloiy 

 should be conchyliology . Conchology is derived from the two 

 Greek words konche, a shell-fish with two valves, and logos, a 

 discourse ; conchyliology from konchulion, which means all 

 sorts of shell-fish, and logos, a discourse. 



