THE FISH-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 sub- 

 sequently 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 color of this species is light red, and the 

 body is nearly translucent. 



Another curious species deserves a word of men- 

 tion. This is the Notodelphys ascidicola, 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 walking or seizing prey, and 

 partly for swimming and breathing. In the first 

 order, the SIPHONOSTOMA, or tube-mouthed En- 

 tomostraca, 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 pur- 

 pose 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 Argulidae, 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 FISH-ARGULUS may be seen upon many of 

 the ordinary river-fishes of England, the stickle- 

 back being its favorite. 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. Argulus foliaceus. B. Caligus Mttlleri. 



C. Nic<5th8 astaci. (Natural size.) 

 D. Nic6tho8 astaci. (Female, magnified.) 

 E. Nic6thog astaci. (Male, magnified.) 



F. Dichelestium sturiduis. 



G. Chondracanthus zei. H. Lernaeodiscus. 



I. Jacculina. 



