1893. THE CLASSIFICATION OF ARACHNIDS. 451 
animals. For example, Simon (11) has recently described a new 
genus Myrtale 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 writer (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 chele 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 Nymphonide, 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. 
1. Pocock, R. I.—Lipfhistius and its bearing on the Classification of Spiders. 
Ann. M. Nat. Hist. (6), vol. x., 1892, pp. 306-314. 
—.—On Some Points in the Morphology of the Arachnida, with 
Notes on the Classification of the Group. Jdid., vol. xi., 1893, pp. I-19, 
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