INTRODUCTION. 25 



such organs, it may reasonably be concluded that the 

 character of the food will be rapidly altered. The 

 fluid from the glands meets the food immediately it 

 enters the stomach of the Caligoicls and acts upon it at 

 once. If blood be the food, the red colour may be 

 destroyed, and give rise to the impression that Cali- 

 goids are not blood-suckers. 



Nothing appears to be known regarding the internal 

 organs of the Copepod Parasites of Fishes with the 

 exception of the Caligoida and Lemma. When the 

 anatomy of all the families has been investigated 

 the food question may be settled. One or two para- 

 sites on a fish may not be hurtful, but when the 

 numbers increase they probably have an irritating 

 effect, and finally, when they remain in one position 

 for some time, the skin and tissues become badly 

 lacerated, giving rise to tumours. The Medesicaste, 

 which lives on the gills of various species of gurnards, 

 occasionally has its head buried in a tumour-like 

 swelling, but we have been unable to determine 

 whether the tumour existed previous to the attach- 

 ment of the parasite or was entirely due to the 

 congestion of the blood-vessels caused by its attack. 

 Gr. H. Drew, in a paper entitled " Some cases of new 

 growths in Fish " (Journ. Mar. Biol. Assoc, n. s., 

 vol. ix, No. 3, June 1912), describes this tumour-like 

 swelling in the gurnard as a case of hsemangiomata, and 

 regards it as probable that the parasite attacked the 

 tumour after it had developed, but we have never come 

 across the tumour without the parasite, or the remains 

 of it, being present. It is quite as likely, therefore, 

 that the hasmangiomata of the gurnard described by 

 Drew is caused by the parasite. (See also our remarks 

 on Lernxa, p. 22.) 



