1894- NOTES AND COMMENTS. 327 



from the one before it, but all constituting a chain that should 

 join, without a single break, two clearly distinct species. Anyone 

 reading the interesting and most valuable book by Mr. Bateson 

 that we review on another page, would suppose that precisely the 

 same difficulty occurred to-day. It is the Discontinuity, as he phrases 

 it, between existing species that has led Mr. Bateson to seek among 

 the facts of variation for some means of overcoming or getting round 

 this initial difficulty ; and he thinks that he has found the solution of the 

 problem in a precisely parallel Discontinuity of Variation. In short, 

 Natiira facit saltwn. 



Now we are not concerned to deny that discontinuous variations, 

 more commonly known as " sports," often occur ; though whether 

 these, under natural conditions, give rise to similarly modified off- 

 spring, such as might be held to constitute a new species, or even 

 variety, is a very different question, that has hitherto been answered 

 in the affirmative only in a very few instances. But this also may 

 pass. What we wish now, is to warn our readers against taking this 

 difficulty of discontinuity too seriously. One noticeable form of 

 advance, during recent years, has been the often successful attempt 

 to work out the problem of the Origin of Species in particular cases. 

 This is not to be done by collecting large numbers of co-existing 

 specimens and arranging them in a line. By such methods discon- 

 tinuity is likely enough to be found even within the limits of a 

 species, as shown in our note on "Mathematical Biology" (vol. iv., 

 p. 83.) The safest, if not the only method, is to take the actual 

 historical facts presented by fossils from successive horizons, eluci- 

 dating them by the facts of individual growth. It is thus that Beecher 

 has traced the evolution of the species of Bilobites(Orthis hiloha), and that 

 Hyatt and others have been able to connect the species of Ammonites, 

 e.g., Coroniceras (Natural Science, vol. ii., p. 279). Even sixteen years 

 ago, in a very remarkable paper on " Transition Forms in Crinoids " 

 [Proc. Acad. Nat. Sci. Philadelphia), Wachsmuth and Springer came to 

 the conclusion that the changes between Burlington and Keokuk 

 species " were made by a series of slow and gradual modifications of 

 specific characters, which correspond m a striking manner with the 

 changes in individual life by growth." To this conclusion, which is 

 supported in the paper by abundant detail, they were led through the 

 examination of a previously unworked passage-bed between the 

 Keokuk and the Burlington. Had this never been discovered, or had 

 it not been so fortunately rich in Crinoids, the species of the Keokuk 

 would be still regarded as " discontinuous " both with one another 

 and with their BurHngton ancestors. 



We cannot give more instances of continuity here. Mr. Bateson, 

 of course, does not dispute them, or if he does, there are plenty more 

 to be found in palaeontological literature, especially of recent years. 

 Neither do we dispute Mr. Bateson's instances of discontinuity. But 

 we do wish to suggest that many cases of apparent discontinuity 



