Morphology of iJie Arachnida. . 9 



which results from the fusion of the tergite and sternite. 

 The other missing tergite is, I suspect, the first. 



Concerning the Palpigradi, an order established by Thorell 

 for the genus Koenenia of Grassi, I can say very little, never 

 having had the good fortune to examine a specimen of tliis 

 group. This curious form seems to lie somewhere between tlie 

 Pedipalpi, especially the Schizonotidas, and the Solifugje. As 

 in the last the abdomen is said to consist of ten segments, but 

 the last three are narrowed to support an antenniform telson 

 as in Thelyfhonus. Moreover, the cephalothorax appears 

 to be segmented very much as in the Solifugte and Schizo- 

 notida3. Unfortunately nothing is known of the breathing- 

 organs of Komenia^ except tlieir reputed absence ; so it is 

 impossible to speculate further as to the true affinities of this 

 genus. 



Kespecting Oihhocellum^ the systematic position of which 

 is a matter of debate, I can suggest nothing new. It is no 

 doubt referable either to the 0])iliones or Pseudoscorpiones, 

 and probably to the former. 



So far the structure of the abdomen has alone been con- 

 sidered. The cephalothorax it is not now my intention to 

 toucli upon, and the homologies of the segments of the 

 appendages have lately been fully discussed by Gaubert. 

 Without either accepting or rejecting the opinion of this 

 author on the subject of the homology of the so-called ^:'a<e//a 

 of the limbs, it may be interesting to state that the segmenta- 

 tion of the second pair or palpi is not to my mind satisfactorily 

 explained on the hypothesis that this segment results from 

 the subdivision of the tihia. For throughout the class of 

 Arachnida — setting aside some aberrant groups — the palpi 

 curiously enough, considering the general plasticity of the 

 limbs, present the same number of segments — namely six. 

 This similarity in the number would lead one to i\\m\'i a priori 

 that the separate segments are numerically homologous each 

 to each throughout the class. So far as the Scorpiones, 

 Pseudoscorpiones, Solifug^, and Pedipalpi are concerned, 

 there can be very little doubt upon this point. But accord- 

 ing to Gaubert this is not the case with the Araneai and 

 Opiliones ; for according to this author the fourth segment 

 or tibia of the palp of e. g. Phrynus is homologous to the 

 fourth and fifth — i\\Q patella and tihia — of the palp of a Spider 

 or an Opilio. But if this is so, the last two segments of the 

 palp of Phrynus are represented by a single segment in the 

 two other groups. That such a double dissimilarity has 

 arisen, I am not at present prepared to believe. 



These considerations, coupled with the great resemblance 



