284 



MANUAL OF ZOOLOGY. 



terior of other animals or adherent to foreign bodies. The 

 young are locomotive, and are -provided with eyes and an- 

 tennae. Branchiae are wanting or rudimentary. 



ORDER I. ICHTHYOPHTHIRA. Adult parasitic, deformed, often 

 with rudimentary limbs ; mouth suctorial ; respiratory organs 

 wanting ; females with external ovisacs. Larva locomotive, and 

 imdergoing retrograde metamorphosis. 



The members of this order (Lerncea, Achtheres^ Peniculus, 

 Caligus, Argulus, &c.) 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, depend- 

 ing from the extremity of the abdomen (fig. 139). Some 



adhere by a suctorial mouth, 

 or by cephalic processes 

 (Cephaluna)\ others are at- 

 tached by a suctorial disc, 

 developed at the extremities 

 of the last pair of thoracic 

 limbs, which are united to- 

 gether (Brachiund) whilst 

 in others (Onchuna) attach- 

 ment is effected by hooks at 

 the free extremities of the 

 first pair of thoracic limbs 

 (Owen). 



The males (fig. 140, b} are 

 usually not attached, but ad- 

 here to the females, of which, 

 from their much smaller size, 

 they appear to be mere para- 

 sites. The chief anatomical 

 Fig. 139. Female of Acktheres Carpenteri, peculiarities of the female are 



magnified. The line placed alongside of ,1 r n TV, l, A \ 



the figure shows the real size, a Abdomen; tllC following I The head IS 



d Disc of attachment developed upon the provided usually with a pair 



last pair of thoracic limbs ; o Ovisac. r j j \i 



of jointed antennae, and the 



body is divided into a cephalothorax and abdomen. The 

 alimentary canal consists of a mouth, gullet, and intestine, 

 terminating posteriorly in a distinct anus. The nervous sys- 

 tem consists of a double ventral cord. There are no differen- 

 tiated breathing-organs, and respiration is effected by the sur- 

 face of the body. 



The embryo (fig. 140, a) is free-swimming, and is provided 

 with visual organs and locomotive appendages. The two 

 sexes are now alike, and the conversion of the active embryo, 



