i893. THE CLASSIFICATION OF ARACHNIDS. 451 



animals. For example, Simon (11) has recently described a new 

 genus Myytale from Madagascar, whose nearest affinities are with 

 Moggridgea from South Africa, and Migas from New Zealand. 



The remarkable group of marine arthropods known as the "sea- 

 spiders " (Pycnogonida) were for long regarded as arachnids by 

 some zoologists, and as crustaceans by others." Of late years, the 

 great authority of Hoek and Dohrn has led to the relegation of these 

 animals to a position independent of either group, indicating their 

 supposed independent descent from vermiform ancestors. Recently, 

 however, Morgan (12) has re-advanced the view of their arachnid 

 affinities, dwelling on the similarity of the polar delamination 

 observed in the division of their eggs to what occurs in the eggs of 

 arachnids, and also on the presence of intestinal branches in the 

 limbs, another arachnid character. The number of appendages is 

 the great obstacle to bringing the pycnogons into line with the 

 arachnids. Their four pairs of walking-legs, their chelate foremost 

 jaws, and their palps are easily represented among arachnids, but 

 what is to be done with the pair of extra limbs, behind the palps, on 

 which the male — a true nursing father in this group — carries the eggs 

 and young embryos ? If we are to retain the pycnogons among the 

 arachnids, we must either derive these extra limbs from a segment 

 which has become aborted in the latter, or else, comparing them 

 with the first pair of legs of a spider, regard the pycnogon's last 

 pair of limbs as belonging to the abdomen. 



The semi-parasitic life of pycnogons on hydroids, polyzoa, and 

 other marine animals has always suggested that they are a degraded 

 group, and degradation often masks affinity. In recent systematic 

 work on pycnogons, Schimkewitsch (13) and the present waiter (14) 

 have directed attention to the relationships between the genera, and 

 the former insists that the most primitive genera are those of most 

 complex organisation. Not only do the number of appendages 

 tend to lessen, the chelae or palpi or both disappearing, but the 

 number of joints in the appendages decreases and the beautiful 

 and complicated serrate processes on the egg-bearing legs in the higher 

 forms — the Nymphonidae, for instance — degenerate into ordinary 

 spines as we descend through the various series. There are few 

 groups of animals in which a comparative study of adult living forms 

 does not suggest the lines upon which progress has been made. In 

 the pycnogons, however, as in most parasitic or semi-parasitic 

 groups, such study can only tell us a tale of decline. 



REFERENCES. 



I. Pocock, R. I. — Liphistius and its bearing on the Classification of Spiders. 



Ann. M. Nat. Hist. (6), vol. x., 1892, pp. 306-314. 

 2. . — On Some Points in the Morphology of the Arachnida, with 



Notes on the Classification of the Group. Ibid., vol. xi., 1893, pp. 1-19, 



pis. i., ii. 



