APPENDIX II 477 



slender form (Eridhonius difformis) inhabits the delicate tubes of 

 a hydroid, while a third (Hyperia medusarum) , as its name signi- 

 fies, lives in the stomach cavity of a jellyfish. The Euthemisto 

 is a surface-swimming amphipod, and in sufficient numbers forms 

 an acceptable meal for hungry fishes, as examination of their 

 stomachs has proven. Gammarus locusta, the common amphipod, 

 or scud, is the most noticeable species of the shore, being very 

 abundant between tide-marks. These creatures are of an olive 

 Igrown or light chestnut-brown colour, much like that of the Fucus 

 they inhabit. They skip about on their sides, and on entering 

 the water swim rapidly with the back downward or sideways. 



The isopods, unlike the amphipods, are flattened above, and 

 are usually of a uniform width throughout their length ; in many 

 cases all their legs are about the same size, whence the name 

 "isopod." They also have sessile eyes and are usually of small 

 size, the largest ones in the Labrador fauna being the two Mesi- 

 dotea, which are about three inches long and taper at the posterior 

 end to a sharp point. The most slender form is Arc-turns baffini, 

 which may attain a length of nearly two inches, with antennae 

 even longer. Several species are parasitic, as the fish-louse, Mga 

 psora, which lives on the skin of the cod and halibut ; the shrimp 

 parasite, Phryxus abdominalis, a hemispherical, distorted little 

 lump of an isopod occurring under the abdomen of various species 

 of Spirontocaris and Pandalus; and a similar but smaller form 

 which attaches itself to the schizopod, Mysis oculata. The last 

 two isopods exhibit great sexual dimorphism, the females being 

 vastly larger than the males and of wholly different appearance. 

 Other parasites belong to different orders of Crustacea. 



The copepods live mostly on the external surface or in the gill 

 cavity of fishes, to which they cling by means of claws and sucking 

 disks. They are represented by Lepeophtheirus salmonis, parasitic 

 on salmon and sea-trout. This species is distinguished in the 

 female by a metallic lustre and by long, slender egg strings. An- 

 other species is Lerncea branchialis, variety sigmoidea, in which the 

 female is fixed in one position for life, having lost all trace of appen- 

 dages save those which fasten her to the host, while the male is 

 reduced to minute size, and, although capable of motion, adheres 

 to some part of the body of the female. 



Occasionally a hermit-crab is infested with one of the Rhizo- 

 cephala (Peltogaster) , parasites which are allied to the Cirripedia, 

 or barnacles, but are degenerate forms with saclike, unsegmented 

 bodies without limbs; their antennas are modified into rootlike 

 processes, which bury themselves in the host, from which they 

 derive nourishment. 



The barnacles reported from Labrador all belong to the sessile 



