444 ^Tr. T. II. Savory 07i the Spider Lipliistius. 



XLTX. — l^he Spider Liphistius : a Studi/ in the Biology of a 

 Friviitive Animal. Bj' T. H. SavORY, B.A. 



A riMMiTlVE animal is of interest either because it represents 

 a "missing link" or because it is a present reminder of a 

 bygone age. The structure of a primitive animal differs 

 from that of its nearest contemporaries in a number of features 

 whicli for various reasons are considered to be of a more 

 primitive character, and hence it furnishes livin<^ evidence of 

 the course that evolution has taken in the group to which it 

 belongs. Moreover, the material providing the evidence is 

 usually obtainable freshly and in quantity, and it can be 

 dissected, and these properties are not shared by the fossilized 

 remains on which much of the geological record is based. 

 Hence tiie emphasis granted to the descriptions of the juiatomy 

 of such familiar primitive animals as Amphioxus, Feripalns, 

 Petroinyzoii, and even Ray Lankester's hypothetical Arche- 

 mollusc. The five weeks' journey of Dr. Wilson, Bowers 

 and Ciierry-Garrard in the Antarctic winter of 1911 — a 

 journey which was probably the most strenuous of its kind — 

 from Cape Evans to Cape Crozier, was made for the purpose 

 of securing embryos of the Emperor Penguin, which is said 

 to be the nearest living approach to a primitive bird. 



In considering the biological significance of a primitive 

 animal, two dangers are at hand. The first of these is the 

 rather too general conception of evolution as a laddei-like 

 ascent of types, or an "end-on" process in which the more 

 specialized exanijdes of one group ultimately gave birth to 

 the less specialized examples of the next. It must be remem- 

 bered that the truth is rather to be found in the idea that the 

 generalized exami)le3 of a group have i)roduced, on the one 

 hand, the specialized examples of that group, and, on the 

 other, the primitive members of the next higher group. 



The second difficulty is to distinguish between the primitive 

 and the specialized characters of the individual animal. 

 Karely can an animal exist for geological ages without 

 showing a specialization in one way or another, which, as it 

 were, compensates for its simplicity elsewhere. It is, of 

 course, a matter of environment and competition, but it is 

 necessary to recollect that an animal is seldom primitive 

 lock, stock and barrel. 



A j)iimitive animal which has been described by a few 

 authors, but which has seldom, if ever, been treated with the 

 fulness it deserves from the broadly biological point of view, 

 is tlie spider Liphistius. A single species was described as 



