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THE AMERICAN MONTHLY [February, 
Notes on Pyenogonida. 
Mr. Francis P. Pascoe, F. L. S., presented a résumé of knowledge regard- 
ing the Pycnogonids at a meeting of the Western Microscopical Club at 
Bayswater, England. Until 1881 but little was known of these animals. In 
that year Dr. Anton Dohrn and Dr. Hoek published two very important 
works. These authors considered the Pycnogonida to form a distinct class 
of the Arthropoda. In old times they were referred to the Arachnida; Lin- 
nzus even placed the few species known to him in the genus Phalangium. 
In later times they were referred by Johnston, Kroyer, and Milne Edwards 
to the Crustacea. Now they are generally classed again with the Arachnida, 
between the mites and the spiders. Haeckel divided the Arachnida into the 
true and the false, the latter comprising the Pycnogonida and the Arctisca 
(water-bears) ; he has since, however, referred the latter to the worms. Mr. 
Pascoe inclines to the view that they are neither crab nor spider forms, but 
he is unwilling to place them in a sort of no man’s land. He has in his 
‘* Zoological classification” included them in the Crustacea. They certainly 
possess eight ambulatory legs, as do spiders, and have a similar arrangement 
of the eyes; other characteristics appear to approximate them more closely to 
the Crustacea. Huxley’s suggestion that their proboscis is formed, as in the 
mites, by the coalesced representatives of the chelicere and pedipalpi, is 
shownby Hoektobeuntenable. Of the eightlegs, which are the main argument 
to prove that they are Arachnida, the first pair, as well as an accessory pair 
between them, are attached to a special or independent segment, and this is 
held to disprove their Arachnidan affinity. The absence of a respiratory 
apparatus is also a condition of many Crustacea, in which, it must be recol- 
lected, the variations of structure are of far higher morphological importance 
than in the other classes of Anthropoda. And so in the Pycnogonida we 
find many of them without eyes, some without mandibles and without palpi, 
the accessory legs sometimes absent in the female—the male only carrying 
the eggs—and the embryo either resembling the larva of the Copepoda in hav- 
ing three pairs of appendages round the mouth (the ambulatory legs being a 
subsequent outgrowth from the body), or the young animal when it leaves 
its larval envelope is already provided with them. The most striking char- 
acter of the Pycnogonida is the small size of the body, it being in some cases 
only about one-sixth the length, and even thinner, than one of the legs; the 
abdomen is reduced to a mere peg-like tubercle. Of the four thoracic segments, 
the anterior is sometimes suturally marked off from the head, but, according 
to Johnston, Savigny has proved that the so-called proboscis is the head, that 
the part behind the proboscis belongs to the thorax, to which the palpi are 
attached, and, consequently, the latter are only modified legs, which, with 
the ovigerous legs, would give seven pairs, or three more than any Arachnidan. 
In consequence of the smallness of the body, the internal organs are almost 
entirely placed in the legs, the stomach sending very long czcz into them. — 
The eggs formed in the legs are emitted through small openings at their base. 
The eyes are the only organ of sense, but they are frequently absent or rudi- 
mentary; when present, they are two or four in number, and, although 
simple, they have an analogy with the compound eye. The nervous system 
consists of a brain and four or five ganglia. There are not many known 
species. We, of the British Islands, have about thirty; a few being found 
under stones in tidal pools, but the majority in the open sea. In the Chad- 
lenger expedition, over a course of 69,000 miles, there occurred only thirty- 
six species. One dredged at 38 fathoms had no eyes, while another, at 1,875 
fathoms, had ‘ two extraordinary large kidney-shaped eyes, directed forwards, 
and two, very small, backwards.’ From 2,160 to 2,650 fathoms, a trifle over 
three miles, the eyes were, in all, rudimentary. Like all long-legged inver- 
