610 



SUPPLEMENT 



" The manner in which this larva treats its 

 prey evinces an extraordinary degree of in- 

 stinct. Many of the creatures on which it 

 feeds are crustaceous about the head and back ; 

 hence they are most vulnerable at the under 

 part of the body. This part, therefore, the 

 larva attacks ; and, to accomplish its aim, 

 swims underneath the intended victim, and 

 bending back its head, is enabled thus to reach 

 its prey by means of its jointed antennas. (The 

 illustrative figure represents a magnified view 

 of the larva taken while young.) Its next 



operation is to pierce its prey with the curved 

 mandibles. Having thus secured its object, 

 it immediately ascends to the top of the water,' 

 and, holding it above the surface, so as to pre-' 

 vent its struggling, shakes it as a dog would 

 a rat. It next inserts the piercer and sucker, 

 (between the mandibles) which are capable' 

 of being thrust out or withdrawn at pleasure. 

 When the juices of the victim are not easily 

 procured by suction or exhaustion, the serrated 

 forceps are employed to tear and masticate it, 

 and thus cause the juices to be more easily 

 obtained. If its food be plentiful, this larva 

 arrives at its full growth in the course of three 

 or four months, and is then nearly opaque and 

 covered with hair. It can be kept several 

 days without food, and by this exinanition 

 its structure becomes considerably more trans- 



parent ; while its natural ferocity w greatly 

 increased, so that it will attack and tight with 

 creatures much larger than itself, and even 

 with its own species. It may be remarked, 

 that it studiously avoids any contest with the 

 nepa, or water scorpion." 



" On a fine sunny day the larvas rise to the 

 surface of the water, and delight to bask in 

 the sun ; but if watched they remain motion, 

 less, with their claws extended. If a stick, 

 or any other substance, be presented to them, 

 they will immediately seize it, and will some- 

 times suffer themselves to be cut into pieces 

 before they relinquish their hold. Their bife 

 has been considered poisonous by m;iny 

 persons, as it takes a greater length of time to 

 heal than other wounds of the same extent : so 

 that caution should be used in taking them. 

 Touching the anatomy of this creature, it may 

 be observed, that the sucker is contained in a 

 crustaceous sheath, and may be considerably 

 protruded or completely withdrawn at the 

 pleasure of the larva : in the annexed cut it 

 is shown extended to about three quarters of 

 its length. The eyes are compound, but of a 

 peculiar formation, consisting of seven oval 

 apertures ranged like leaves upon a branch. 

 The whole of the head and thorax are curi- 

 ously marked with a number of lines and 

 spots. The legs are six in number ; they are 

 thickly set with rows of hair on their opposite 

 sides, and each is furnished with a sharp claw. 

 The number of swimmers on each side is 

 seven ; they are covered with hairs, and to 

 the specimen from which the drawing was 

 taken, a vast number of vorticellce convcllaricB, 

 or bell-polypi, were attached. These will be 

 recognized in a subsequent engraving by their 

 bell-shaped figure. They sometimes infest 

 this species of larvae to such a degree as con- 

 siderably to impede its motion in swimming. 

 On each side of the abdomen, which com- 

 mences near the origin of the first pair ol 

 swimmers, arise the great tracheae, or air- 

 vessels, distinguished in the cut by a deeper 

 shade than the other parts; the two approach 

 each other near the tail, where an exceedingly 

 curious process is also distinctly exhibited. 

 The whole surface of the body is thickly 

 covered with hairs, and several tufts are dis- 

 posed in clusters with some regularity, down 

 the back and sides. The flexible pulsatory 

 organ, or dorsal vessel, situated at the lower 

 part of the body, is in perpetual motion. Its 

 form somewhat resembles the letter S inverted : 

 it however varies a little during its vibrating 

 motions. The use of the curious appendages 

 at the lower extremity of the body is unknown. 

 Its tail is bi-forked and crustaceous, and is 

 marked as shown in the cut. The short 

 line shows the natural size of the larva, 

 at the same period of its growth as that at 



