INTRODUCTION. 23 



marked by fine transverse lines. The colour of the 

 animal varies from dark violet to light red. The 

 alimentary canal is similar in structure to that of 

 the adult Lepeophtheirus. A large digestive gland 

 occupies each side of the cephalo-thorax. The 

 nervous system of the Lernaean cyclops is practically 

 similar to that of the adult Lepeophtheirus. The 

 ovaries occupy a normal position. 



At the conclusion of its pelagic life the Lernaean 

 cyclops fixes itself to the gills of a fish, and the retro- 

 gressive metamorphoses commence. The parasite 

 buries its head in the tissues of the host and then 

 develops three horns. The horns are simple at first, 

 but by gradual division they acquire the adult type. 

 The genital segment elongates very considerably. 

 The eyes, antennules, antennae, mandibles, maxillae, 

 and one pair of maxillipeds completely disappear. 

 One pair of maxillipeds persists all through life, and 

 is represented in the adult by a pair of small hooks 

 placed under the mouth. 



The next phase, represented on Plate XLII, shows 

 that the development of the horns, the disappearance 

 of the various appendages, and the great lengthening 

 of the genital segment are followed by a looping of the 

 posterior region at that segment. This loop gradually 

 expands, and finally takes on the adult condition. 



The Food of the Parasites. 



There appears to be considerable doubt regarding 

 the precise food of the Copepod Parasites of Fishes. 

 Some authors conclude that, because no red colour can 

 be seen in the alimentary canal, such families as the 

 Caligoida feed entirely upon the mucus of the host's 

 body. It has been suggested, therefore, that Lepeo- 



