Guide to Arachnida . 
Table-case 
No. 26. 
116 
just behind the last, are used, in the male sex, for carrying the eggs, 
and are known as “ ovigers.” One or other of the first three pairs, 
or (in the female sex) all of them, may be absent in certain genera. 
The apparent resemblance of a Pycnogonid to an Arachnid is 
due chiefly to the four pairs of long and slender legs, and to the 
chelate form of the first pair of appendages. The comparison, 
however, is complicated by the fact that the Arachnida possess but 
one pair of appendages, the pedipalps, between the chelicerae and 
the first legs, while the Pycnogonida have two pairs, the palps 
and the ovigers, in the same position. A further serious difficulty 
in the way of comparison is 
raised by the existence, in 
Antarctic seas, of two genera, 
Decolopoda (Fig. 79) and 
Pentanymphon, which have 
five, instead of four, pairs of 
legs, and four free somites 
behind the head. 
The internal structure 
presents many exceptional 
features, which are illustrated 
by the drawings exhibited 
above the Table-case. The 
food-canal sends long diver- 
ticula into the appendages, 
and the generative glands also 
are partly situated in the legs 
and open to the exterior by 
pores on the second segments 
of some or all the pairs. A 
remarkable fact in the breed- 
ing habits of these animals is 
that the eggs are carried, after deposition, not by the female, but 
by the male, attached in clusters to the third pair of appendages. 
The Pycnogonida are all marine animals, ranging from shallow 
water to depths of at least 2,000 fathoms. They are especially 
abundant in the Arctic and Antarctic regions. The specimens ex- 
hibited include Pycnogonum littorale , which is common between tide- 
marks on the British coasts ; Nymphon (. Boreonymphon ) robustum 
(Fig. 78), a characteristic Arctic species ; two species of the deep-sea 
genus Colossendeis, which includes the largest of the Pycnogonida; 
and the ten-legged Pentanymphon and Decolopoda already alluded to. 
Fig. 79. 
Decolopoda australis, a ten-legged 
Pycnogonid from the Antarctic Seas. 
Slightly reduced. [Table-case No. 26.] 
