HA RD WICKE'S SCIENCE- G OSSIF. 



;o7 



This species resembles very closely the widely dis- 

 tributed J/, corniita and differs from it principally in 

 being about one-fourth smaller, and rather narrower 

 in proportion, and in having both the anterior edges 

 of the lorica excised and to a greater degree. Mr. 

 Gosse states that in M. cornuta the front of the lorica 

 is shallowly incurved, that the anterior dorsal edge is 

 slightly less incurved than that of M. hmaris, but 

 that the ventral edge has its margin quite straight. 

 I think that here he is slightly in error, and partly on 

 this account, and partly for the sake of comparison 

 with the figure of the new species, I add an outline of 

 the ventral aspect of the lorica of M. cor?mta when 

 retracted. This position (not figured by Mr. Gosse) 

 shows the straight occipital edge and the very slightly 

 excavate pectoral edge of the lorica as well as the 

 large basal foot-joint. In the numerous examples I 

 have examined, the occipital edge has always seemed 

 straight and the pectoral slightly excavate, and this 

 structure is exactly what would be necessary to 

 facilitate the bending downwards of the head. 



In any case, in M. arcuata, the excision of both 

 anterior edges is much sharper than in M. lunaris. 

 In all other details, in general aspect when extended, 

 and in its sluggish habits, the species is the counter- 

 part of M. cormtta, yet the differences noted, though 

 minute, are constant, and I consider fairly entitle the 

 form to rank as distinct. 



Mr. Gosse gives the length of M. cornuia as 

 135 inch extended. The largest specimens I have 

 measured were about ^^Ij inch, and the average -^^^ inch, 

 while M. arcuata in the like position averages 

 5^3 inch, the lorica alone being about jig inch. I have 

 found dead specimens very abundantly among the 

 drainings from Sphagnum and I have recently had 

 for a little time a colony in a jar, the bottom of which 

 was covered with some threads of moss, gathered last 

 year and now springing into fresh growth. 



My sketches show a broad and a narrow form, 

 apparently the extremes of variation, the former being 

 probably a more mature individual. Young speci- 

 mens resemble when slowly gliding along, the form 

 which I take (yet with some doubt) to be the M. 

 mollis of Mr. Gosse, which however when in retrac- 

 tion s not to be distinguished from M. cornuta and is 

 therefore equally distinct from the present. 



Habitat among roots of Sphagnum, Epping Forest. 



NEC-DARWINISM. 



By A. G. Tansley. 



I. — The Question at Issue. 



A RE we still justified in holding Mr. Darwin's 



l\ conclusion that "habit, or use and disuse, 



have in some cases played a considerable part in the 



modification of the constitution and structure ; " * or 



should we rather consider, with a more modern 



' Origin of Species, ".6th edition, p. 114. 



school of naturalists, that this supposed factor in the 

 transmutation of species is unproven and unnecessary ; 

 unproven because the hereditary transmission of 

 characters acquired during the lifetime of the indi- 

 vidual has never been experimentally established, and 

 unnecessary because we can explain the phenomena 

 of organic evolution without invoking its aid ? 



Such is the question which, of all others, is now 

 engaging the attention of the biological world. 

 Closely connected with it is the consideration of 

 Professor Weismann's brilliant contributions to the 

 existing literature of variation and heredity, including 

 a theory of heredity absolutely inconsistent with the 

 conclusion of Mr. Darwin which we have quoted. 

 For the last two years and a half, that is since the 

 discussion on the transmission of acquired characters 

 raised by Professor Ray Lankester at the Manchester 

 Meeting of the British Association in 1887, in 

 which Professor Weismann himself took part — this 

 subject has been prominently before English natu- 

 ralists. During this period there has been no paper 

 or discussion on the subject, hardly even a reference 

 to it, in the pages of Science-Gossip.* It is 

 obvious that the question is one of the deepest 

 interest, affecting, as it does, the very foundation of 

 our conception of organic evolution. If the " La- 

 marckian" factor, as it is sometimes called, is a true 

 factor, it must have played an important part in the 

 modification of species. If we are to reject it alto- 

 gether, a large number of phenomena will have to be 

 explained in other ways ; in fact its rejection will en- 

 tail a more or less important modification of the 

 Darwinism of Mr. Darwin. Apart from these con- 

 siderations. Professor Weismann's theories of heredity, 

 variation, etc., which differ essentially from those 

 hitherto generally held, are concerned with matters 

 lying at the root of any explanation of evolution. I 

 therefore thought that a series of papers on the 

 subject, which should aim at setting forth, as briefly 

 as possible, the various problems involved, would be 

 of interest to those readers of Science-Gossip who 

 may lack the time or inclination to study the subject 

 more deeply. The method I propose to pursue is, 

 first to state clearly the main question at issue, which 

 turns on the truth or falsehood of what is known as 

 Lamarck's "second law," and to sketch the present 

 position of opinion upon -it, then to give an outline of 

 Professor Weismann's hypotheses on the subject of 

 heredity and variation, and finally to try and show 

 the exact bearing of these theories on the question 

 with which I started. 



We will commence our brief account of the position 

 of opinion on the subject under discussion, and of 

 how it came to be what it is, by stating the question 

 at issue and then defining our terms. The question 

 in its most general form is: "Can an 'acquired' 

 character be inherited ? " 



* The above was written in April, 1890. 



