290 Transactions. 



finally freed from the exoskeleton, though only about half of them were 

 drawn out. At the end of four hours the movements were growing very 

 feeble, and at the end of the fifth hour, as a fairly long struggle produced 

 little result, the animal evidently was too exhausted to continue. There 

 was just a feeble movement kept up for another hour, and then the struggle 

 was over and the animal dead. With its partially cast shell it has been 

 preserved carefully for future reference. 



The following morning, in another bowl, another animal was seen to be 

 dragging round with it an exoskeleton attached to one corner of its carapace. 

 The exoskeleton was rather imperfect, as though in its endeavours to free 

 itself the animal had become entangled in it and brcken it. An attempt 

 to assist the animal to get rid of its burden resulted in its death ; probably 

 the soft tissues of the carapace were injured. In this case the. animal 

 remained on its back, feebly kicking, for more than a day, and then died 



In one or two instances the cast shells removed from the water were 

 complete ; in other cases the carapace had broken away frcm the body- 

 cuticle. In one such case, on removing the carapace-cuticle from the water, 

 it was seen to be in two layers, which were joined at the posterior end but 

 completely separated right round the edge of the curve from one posterior 

 angle to the other. In the lower layer was a tear in the tissue to allow of 

 the body being drawn through. 



I have not been able to find any record of the method of moulting for 

 Lepidurus or Apus, but Packard (1882, p. 412), quoting from a letter from 

 Dr. Gissler, " who has raised the young Apus from the egg," says, " I am 

 certain that the larvae of Apus (from skins examined) split across or just 

 in front of the eyes, and with two or three jerks the animal rids itself of 

 the underlying skin." According to Packard, then, this corresponds to the 

 method of moulting in Limulus. 



Movements. 



Most of these lower forms of Crustacea usually swim on their back, a 

 method adopted probably for the protection of the soft tissues of their 

 limbs from the attack of their fellows or other inhabitants of the water. 

 Spencer and Hall (1896, p. 228) report an instance of this from Australia : 

 " While watching Apus swimming about, one was seen to come suddenly 

 to the surface struggling violently, and on being caught was found to have 

 three water-beetles tearing its soft appendages. These beetles are always 

 darting up and down in search of food, and if the Apus swam with its 

 ventral surface downwards it would probably more often fall a prey to 

 such voracious enemies." 



In the case of the living animals of the genus Lepidurus kept in the 

 laboratory, they were more often to be seen ventral surface downwards, 

 swimming or paddling along in the mud at the bottom of the bowl. At 

 first some of them were very active, and their movements were interesting 

 to watch as they darted here and there in th.e water, steering themselves 

 by the posterior portion of the body, and avoiding as far as possible their 

 fellows. Occasionally they would attempt to nibble at the cercopoda or 

 caudal setae of another, and would then be shaken off. 



In conclusion, it might be well again to draw attention to the fact that 

 several zoologists have expressed the opinion that the number of the species 

 of Lepidurus would bear reduction. Some of the specific characters used 

 vary considerably in individuals taken from the same locality and even 



