CRUSTACEANS 



appendages that precede the pleon. Byerley speaks of Limnoria lignorutn 

 (J. Rathke), the gribble, under the later and now discarded name L. terebrans, 

 and says that ' the wooden piles of the Rock lighthouse are completely drilled 

 by this species.' ^ Mr. Andrew Scott, discussing surface collections in the 

 vicinity of the Lancashire coast, says ' On a warm day, when the sea is calm, 

 numbers of Eurydice may be seen disporting themselves on the surface. In 

 their movements they are not unlike the " whirligig " beetle of the freshwater- 

 ponds.'^ The species is not specified, but probably Eurydice achata (Slabber), 

 often called E. pulchra (Leach), was the one observed. It is a curious cir- 

 cumstance that dead specimens of this family when put into liquid often 

 display the same whirligig movements as those executed by the live animals, 

 from which it may be inferred that, when the creature is introduced to the 

 surface film of the water, the structure of its body has something to do with 

 the mode of motion independently of its will. Mr. A. O. Walker mentions 

 Sphceroma serratum (Fabricius) from the stomach of a cod at Piel Island, and 

 from that of a whiting at Morecambe, and Idotea marina (Linn.), also from a 

 whiting at Morecambe. Though it does not seem to be specially recorded, 

 the occurrence of Hemiartbrus abdominalis (Kroyer), so commonly parasitic 

 beneath the pleon of Pandalus montagui, may almost be taken for granted. Of 

 terrestrial Isopoda, or woodlice, strange to say, I have only found a single 

 record, that of Oniscus murarius, another name for the very common O. asellus 

 (Linn.), which Byerley oddly includes among the ' Myriopoda,' with the 

 unimpeachable comment that it is ' very abundant about walls, rubbish, and 

 damp localities.' * 



The Amphipoda are associated with the Isopoda in classification on 

 account of certain obvious points of resemblance. The two sub-orders, 

 besides being alike edriophthalmous or sessile-eyed, agree also in the distinctly 

 tri-partite arrangement of the body. The consolidation of head and trunk 

 which prevails in crabs and lobsters here gives place to a severance of the 

 cephalic division from a seven-segmented middle body or person. The 

 Sympoda make an approach to this arrangement by having five segments 

 between the head and tail uncovered by the carapace. It is these five 

 segments which throughout the Malacostraca must be considered as normally 

 leg-bearing segments. But in the Isopoda and Amphipoda the two pre- 

 ceding segments also carry legs, instead of having their appendages, as 

 generally elsewhere, converted into mouth-organs. In some respects, however, 

 the Amphipoda differ greatly from the Isopoda. They are usually com- 

 pressed from side to side instead of being dorso-ventrally depressed. The 

 appendages of the pleon are three pairs of pleopods with rami, as a rule 

 flexible and many jointed, and three pairs of uropods with inflexible rami, 

 not many jointed. In the Isopoda there are five pairs of pleopods and one pair 

 of uropods, the flexible many-jointed condition being found only in the 

 uropods, and there as an anomalous character. Above all, the Amphipoda 

 are distinguished by the simple, or comparatively simple, branchial vesicles 

 attached to some limbs of the person, and by the forward position 

 of the heart, in contrast to the Isopoda, among which the heart (except 

 in the anomalous group) is carried towards the rear in connection 

 with the branchial system of the pleopods. When diligently searched 



1 Fauna of Liverpool, 56. 2 7>a»/. Liverp. Biol. Soc. viii. 96 (1899). * Fauna of Liverpool, 1 1 1, 



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