INTRODUCTION. 19 



securely attached to its host by strong branched horns 

 which are buried in the tissues of the gill-arches. In 

 many cases the head will be found to have actually 

 penetrated the ventral aorta. The specimens can 

 only be removed from the host by careful dissection. 

 Any attempt to remove them by force results in the 

 head being left in the tissues. The parasite, when once 

 fixed, remains in the same position throughout life. 

 When it dies the softer parts decay, but the head 

 remains embedded in the tissues of the host. The 

 heads of dead parasites are frequently met with when 

 dissecting-out living specimens. 



The adult female is cylindrical and is a little over an 

 inch in length. It is unsegmented, but can be roughly 

 divided into three parts — a globular head with anchor- 

 like processes, a narrow neck, and a much swollen 

 posterior part. The globular head corresponds to the 

 anterior region of the cephalo-thorax in Lepeoplitheirus. 

 It is furnished with three more or less branched horns 

 which are outgrowths from the cephalo-thorax. The 

 head is slightly curved downwards and terminates in 

 a conical apex. The anterior portion of the neck 

 represents the remainder of the cephalo-thorax and 

 the fourth thoracic segment. The remainder of the 

 neck and the greater part of the swollen mass behind 

 correspond to the genital segment of Lepeophtheirus. 

 The abdomen is represented by the terminal portion 

 of the swollen part, which gradually tapers to a blunt 

 end. The whole of the swollen part is bent into the 

 form of the letter S. The neck is marked by fine 

 transverse lines. 



The appendages are rudimentary, the greater number 

 being entirely absent. The appendages present are a 

 pair of maxillipeds immediately under the mouth and 



