. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. ANNULOSA : CRUSTACEA. 2O9 wanting, but are primitively natatory. Not only does their de- velopmental history bear out this view, but cases are known (in some Zernaa) in which the males do not undergo retrograde metamorphosis, but remain permanently in the condition of free Copepods. This division includes the single order Ichthyophthira, tine characters of which are therefore the same as those of the sub- class, comprising various parasites upon fishes belonging to the genera Ler
. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. ANNULOSA : CRUSTACEA. 2O9 wanting, but are primitively natatory. Not only does their de- velopmental history bear out this view, but cases are known (in some Zernaa) in which the males do not undergo retrograde metamorphosis, but remain permanently in the condition of free Copepods. This division includes the single order Ichthyophthira, tine characters of which are therefore the same as those of the sub- class, comprising various parasites upon fishes belonging to the genera Lerncea, Achtheres, Peniculus, &c. Order I. Ichthyophthira.—The members of this order are attached in the adult condition to the skin, eyes, or gills of fishes, and when mature possess an elongated body, having a more or less distinct head, and in the females usually a pair of long, cylindrical ovisacs, depending from the extremity of the abdomen. Some adhere by a suctorial mouth, or by cephalic processes {Cephalund) ; others are attached by a suctorial disc, developed at the extremities of the last pair of thoracic limbs, which are united together {Brachiuna); whilst in others ( Onchu- na) attachment is effected by hooks at the free extremities of the first pair of thoracic limbs.—(Owen.) The males are usually not attached, but adhere to the fe- males, of which, from their much smaller size, they appear to be mere parasites. The chief anatomical peculiarities of the female are the following:—The head is provided usually with a pair of jointed antennae, and the body is divided into a cepha- lothorax and abdomen. The alimentary canal consists of a mouth, gullet, and intestine, terminating posteriorly in a distinct anus. The nervous system consists of a double ventral cord. The embryo (fig. 63, a) is free-swimming, and is provided with visual organs and locomotive appendages. The two. Fig 63.—Ichthyophthira. a Free-swimming \xrvi. ai Achtheres^rcanim, in its first stage
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Keywords: ., bookauthorni, bookcentury1800, bookdecade1870, booksubjectzoology
