106 ZOOLOGY. 
living bodies unlike the females, but somewhat like the young, and these he 
considered males, a view in which Kroyer concurs. These males are 
much smaller than the females, and those of different species resemble each 
other, even when the females are quite dissimilar. 
When the young leave the egg, they bear a remarkable resemblance to 
those of Cyclops, Apus, and other undoubted Crustacea. They have a 
large eye, a pair of antenne, two pair of large swimming feet, by means of 
which they swim through the water until they find a proper station to which 
they can attach themselves, as already described in the Cirrhopoda, and 
other groups of the lower animals. As in the higher forms, they moult 
frequently during their growth. After affixing themselves, the feet disappear, 
or are transformed into foot-jaws or other organs adapted to their new mode — 
of life. The eye being now useless, disappears also. In some, two long 
arms appear (see the inverted jigs. 30, 31), which are united at the apex, 
where they form a sucking cup, with its concavity armed with teeth, 
forming an organ which is immersed into the flesh of fishes, and is used in 
maintaining the place of the animal. This metamorphosis, by which an 
animal is apparently less perfect in the adult state that when a larva, is 
styled retrogressive by Burmeister. 
In the annexed figure, a represents the young, 
and 6 the adult female of Lerneocera, a genus 
named from the horn-like projections upon the 
head. The body is slender, the feet are entirely 
absent in the adult, and the thorax includes most 
of the body, the abdomen being very small. ZL. 
cyprinacea (6) is about eight lines long, and 
was discovered by Linneus, in 1746. Figure 
ce represents the male, and d the female of 
Anchorella uncinata. The former is globular, 
and affixes itself by means of two pairs of hooks. The rudimentary 
abdomen of the latter is at the base of the egg sacs. It is one fourth of a 
iine long, whilst the female is six or eight lines. The long projection in 
the figure of the latter represents the arms. This species is found upon 
the fins and gill covers of the cod and haddock. 
_ Achtheres percarum (pl. 78, fig. 31), the female of which is two lines 
long, affixes itself to the tongue, inside of the mouth and eyes of Perca 
Jlwiatilis. The alimentary canal is straight, without any division between 
stomach and intestine, and the nervous system is said to consist of a longi- 
tudinal cord on each side of it. 
The Caligide are distinguished from the Lernwide by the better 
developed organs of motion. The foot-jaws are well developed, and the 
thorax has several distinct rings and pairs of feet. Like the preceding 
family, this one is divided into several sub-families. Caligus (pl. 74, jig. 
34) has avery large depressed circular head, with large frontal plates having 
a sucking disk laterally beneath. There are eight feet, and the antenne are 
small and bi-articulate. They inhabit the sea, and affix themselves, with 
the aid of their foot-jaws, to the body or branchial cavities of fish. They 
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