THE EISH-ARGULUS. 



639 



surface, and in a few minutes, when it "becomes still, they can be seen ascending slowly, 

 but rarely using the antennae. I could only obtain specimens by including them in 

 a large quantity of water taken up suddenly, from which they could be separated 

 subsequently by straining through a calico bag. A bucketful (two gallons) of water often 

 produced twenty to thirty individuals, and sometimes twice that number. They 

 never survived a single night, even though kept 

 in their native element in a vessel. From their 

 constant darting from side to side of the vessel, 

 perhaps it is a safe inference that the fear of 

 danger in their new situation may be one of the 

 chief causes of the early extinction of life." 



The colour of this species is light red, and the 

 body is nearly translucent. 



Another curious species deserves a word of 

 mention. This is the Notodelphys aseidicola, which 

 is found swimming in the bronchial sac of the 

 ascidia. 



IN this illustration we have examples of a 

 group of Entomostraca which are parasitic upon 

 fish and other inhabitants of the waters. They 

 belong to Dr. Baird's third legion, called the 

 Pcecilopoda, a term derived from two Greek 

 words, signifying various - footed. They are so 

 named because they are partly formed for walk- 

 ing or seizing prey, and partly for swimming 

 and breathing. In the first order, the SIPHONO- 

 STOMA, or tube-mouthed Entomostraca, the mouth 

 is furnished with a tube containing sharp spike- 

 like mandibles. The foot-jaws are well formed. 

 The object of the tube and its sharp mandibles 

 is evidently for the purpose of piercing the skin 

 and sucking the juices of the beings upon which 

 they cling, and the strong foot-jaws enable them 

 to hold so firmly that they cannot be shaken off. 

 The first tribe is called Peltocephala, or buckler- 

 headed, because the head is shaped something 

 like an ancient buckler ; the head is also furnished 

 with plates in front, and small antennae of two 

 joints. The first family of these creatures is 

 called ArgulidDe, and may be known by the 

 circular shaped head shield, and the manner in 

 which the second pair of foot-jaws are modified 

 into a pair of powerful suckers. 



The EISH-ARGULUS may be seen upon many 

 of the ordinary river-fishes of England, the stickle- 

 back being its favourite. I have seen it on the 

 roach, and even upon the golden carp. It is not 

 very small, being about the diameter of a small 

 sweet pea, and may easily be watched if placed in 

 an aquarium in which any fish are swimming. 

 The little creature at once makes for the fish, 



darting along with considerable speed, and fixes itself to the side just under the pectoral 

 fins. It does not, however, remain fixed to the fish, but occasionally leaves it, and 

 starts off on little voyages of discovery, always, however, returning at short intervals, 

 as if for the purpose of assuring itself of a meal. It is wonderfully flat, looking very 



A. "Arguing foliaceus. B. GaUgus Miilkri. 



C. Nicdthoe dstaci. (Natural size.) 



D. Nicdthoe dstaci. (Female, magnified.) 



B. Nicdthoe dstaci. (Male, magnified.) 



P. Diclwlestium sturidnis. 



Q. Chondracanthus zei. H. Lerwzodiscus. 



I. Jacculina. 



