246 HALF AN HOUR WITH CRUSTACEA. 



gonidtte. They seem to affect the bushy tufts of the 

 common coralline sea-weed. In appearance they are 

 not unlike those marine crustaceans which go by 

 the name of " Sea-spiders." They are furnished 

 with hooked claws, instead of nippers, by means of 

 which they are able to cling very tenaciously to any 

 object. One of these (Pallene pygmsea, Fig. 132) 

 produces larvae which have the two foreclaws, how- 

 ever, provided with nippers. When placed under the 

 microscope the movements of the stomach, &c., can be 

 plainly seen, owing to the transparency of their bodies. 

 Their ova is attached to the abdomen by means of 

 false feet. They do not seem to be provided with 

 any special organs of respiration, but the oxygenation 

 of the blood appears to take place through the 

 general surface of the body, which is provided with 

 perforations set in minute tubercles that are scattered 

 all over it, like the spiracles of an insect. Notwith- 

 standing this, the articulation of the limbs to the 

 body is by means of stout and strong muscles, 

 every movement of which can be seen through the 

 transparent integument. An allied species is Achelia 

 liispidata, Fig. 133, which may be known by its 

 smaller and more compact body, and shorter limbs, as 

 well as by its proboscis. It also possesses a small pair 

 of jointed antennas. Both the foregoing little crea- 

 tures live on decaying animal and vegetable matter. 

 The true Pycnogons, or "Sea-spiders," are now 

 classed as genuine crustaceans by Dr. Dohrn, who has 

 written on their embryology. One of them (Nymphon 



