TUE ISOPOD GE^fITS OUROZEUKTES. 338 



between these to form the calcified parts of the foliaceoiis 

 oostegites. 



While the first tergum is, as already stated, prolonged forward 

 GO each side of the head, the last has a similar tendency to the 

 horseshoe form, its lateral areas spreading back round the base 

 of the abdominal region. Of the remainder the second, third, 

 and fourth are considerably longer antero-posteriorly than the 

 fifth, sixth, and seventh. 



The seven pairs of limbs are all constructed on the same plan. 

 A large flattened basipodite (to which is fused a small round 

 coxopodite fitting into the limb-socket) is followed by an ischio- 

 podite, three approximately equal joints, and a curved claw. 



The flattening of the basipodite increases from before back- 

 ward, and in the last four pairs the ischiopodite also becomes 

 increasingly lamellar, so that these hinder limbs are very efficient 

 swimming-organs. 



The remaining structures belonging to the thoracic region are 

 the large foliaceous plates or oostegites, which together form the 

 great brood-chamber below the body of the animal, in which the 

 eggs and embryos pass through their successive developmental 

 stages. It is of course well known that such a structure occurs 

 in many genera of Isopods and, with little difference, of Amphi- 

 poda also ; but I have not as yet met with any description of 

 one so large or fully developed as that now under consideration. 



There are four of these large oostegites or plates, as they may 

 be called for the sake of brevity, on either side of the body 

 passing round from the line of the limb-sockets toward the 

 ventral middle line, where the series on the left side overlaps that 

 of the right. 



It is to be noted, however, that these plates have no con- 

 nexion with the limbs themselves. The calcification which 

 supports their basal and central parts is prolonged down from 

 the epimera, usually from the thickening in front of the limb- 

 socket ; so that the free movement of the limbs in no way 

 interferes with the rigidity of the walls of the chamber (PI. XIV. 

 fig. 11). 



I mention this specially, as the usual descriptions in our text- 

 books, — such as " brood-lamellae attached to more or fewer of the 

 thoracic limbs,"* or " thoracic legs ... in the female some of 

 them provided with delicate membranous plates (oostegites) which 



* ' Forms of Animal Life,' Rolleston-Jackson, 1888, p. 537. 

 LIXIf. JOUEN. — ZOOLOGY, VOL. XXT. 27 



