IIG 



Guide to AracJinida. 



Table-case 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, 

 Decoloijoda (Fig. 79) and 

 Pcntmujmphon, 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 

 l)y 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 P?/c?io^o?mm littorals, which is common between tide- 

 marks on the British coasts ; Nymplion {Borconymphon) robustiim 

 (Fig. 78), a characteristic Arctic species ; two species of the deep-sea 

 genus Colosscndeis, which includes the largest of the Pycnogonida; 

 and the ten-legged Pcntanymplion and Decolopoda already alluded to. 



Fig. 7'J. 



JJccolopoda australif;, a teu-legged 



Pycuogonid from the Antarctic Seas. 



Slightly .reduced. [Table-case No. 26.J 



