328 - MR. H. M. BEEXAED ON THE 



Takino- the limbs as a wholCj the variations are considerable, and no single Arachnid can claim to have 

 retained the primitive conditions. It seems only possible to deduce them separately from a primitive 

 ancestral form in which the limbs were evenly developed and evenly arranged along the two sides of the 

 body, separated by a median row of sternal plates, as shown in the diagram (PI. XXIX. fig. 14). 



The character of the limbs, suggested in this diagram and in figure 5, PI. XXIX., is not unlike that of 

 the ambulatory limbs of the Silurian Scorpion Paheophonus (PI. XXVII. fig. 10), whose semiaquatic, 

 i. e. littoral, existence makes its retention of the primitive type of ambulatory leg not improbable. 



Vestiges of Abdominal Appendages. — CareM study of the ventral surfaces of Galeodiclae 

 has led me to the conclusion that the " sterna " along the ahdominal segments 

 represent rudimentary limbs which have simply flattened down. 



Figs. 6, 7, 8, 9, 10, PL XXIX., show a continuous series of plate-like structures 

 on the abdominal segments bearing all the characters of vestigial appendages. That 

 these are the vestiges of limbs which formed at one time a continuous series with those 

 on the cephalothorax we gather from the following facts : — 



(a) Fig. 7, PI. XXIX., shows a chitinous fold across the genital operculum, repeating 

 the interarticular fold of the preceding appendage (<?/, diagram, PI. XXIX. fig. 11). 



(5) The genital opercula are generally admitted to be vestigial appendages. The two 

 pairs of stigmatic opercula repeat the genital opercula so closely that they must also be 

 vestigial appendages. These are followed by a series of six plates, the first three of 

 wliich may at once be claimed as vestiges, inasmuch as six pairs of limbs are almost 

 universally admitted to have been present on the abdomen of Arachnids. But we 

 have here in all nine pairs of plates obviously forming a homonomous series. If the 

 first sis of these are vestiges of limbs, we may safely conclude that the last three are so 

 likewise (compare especially figs. 8, 9, 10, where the plates repeat exactly the stigmatic 

 opercula). 



(c) These vestiges are often covered with hair diff'ering entirely from the hair on the 

 rest of the abdomen, but repeating exactly the character of the hair on the coxse of the 

 cephalothoracic limbs. 



{d) The same is the case with colour. These vestiges often differ very markedly in 

 colour from the rest of the abdomen, and from the terga, but repeat exactly the colour 

 and general appearance of the coxse of the cephalothoracic limbs. 



[e) These vestiges meet in the middle line like the coxce of the cephalothoracic limbs, 

 while internally the dorso-ventral muscles, which in other Arachnids (e. g. Scorpio) are 

 attached just inside the areas which admittedly represent vestiges of the limbs associated 

 with the lung-books, in Galeodes meet in the middle line. 



(/) The stigmatic apertures, which are always associated with rudimentary limbs, 

 have also moved into the ventral middle line. 



These arguments and figures leave, I think, little doubt that there were once at least 

 nine pairs of limbs on the abdomen of Galeodes, but none of the vestiges any longer 

 appear as limbs. The genital and stigmatic opercula are now nothing more than folds, 

 while the following vestiges are flattened completely down and look like sternal plates. 



On the posterior edges of the stigmatic opercula in the genus Galeodes, a row of short 

 stout spines occurs, the paired origin of which is obvious (PL XXIX. fig. 10). These 



