106 ZOOLOGY. 



living bodies nniike the females, but soinewLat like the young, and these he 

 considered males, a view in whicli 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 antennae, 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 figs. 30, 31), which are united at the apex, 

 where they form a sucking cup, with its concavity armed with teeth, 

 formino- an orsan 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 h the adult female of Zernceocera, 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. Z. 

 cijjyrinacea (b) is about eight lines long, and 

 was discovered by Linnaeus, in 1746. Figure 

 c represents the male, and d the female of 

 Anchorclla 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 

 line 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 peTcarum {pi. 78, jig. 31), the female of which is two lines 

 long, affixes itself to the tongue, inside of the mouth and eyes of Perca 

 fluviatiUs. 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 Caligidm are distinguished from the Lerncddce 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 {pi. ^i-^^fig. 

 34) has a very large dejiressed circular head, with large frontal plates having 

 a sucking disk laterally beneath. There are eight feet, and the antennas 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 

 310 



