1887.] 



ON CYCLESTHERIA HISLOPI. 



53 



claws are distinctly marked off from the plate, though as yet rather 

 short ; behind the last pair of dorsal spines, present in the former 

 stage, three or four other pairs have appeared, all however 

 still very small. The shell has very much increased in size, so 

 as now to obtect the greater part of the trunk and head together 

 with their appendages, though as yet by no means admitting 

 of the whole body being withdrawn between the valves. 



Although the young in the last-described stage exhibit all 

 essential parts found in the adult animal, most of which, moreover, 

 have commenced their functional activity, they are as yet far 

 from ready to leave the incubatory cavity of their mother. This 

 does not take place before the young have attained a fuller 

 development, so as in every respect, except size, to agree with the 

 adult animal. When this period has arrived, the parent animal 

 is found to curve its trunk strongly downwards, whereby the incu- 

 batory cavity becomes opened posteriorly. Through this opening 

 the young escape, but generally not all at the same time, one or 

 two being discharged at shorter or longer intervals. When just 

 hatched the young have a length of about 1,20 mm., or nearly 

 of the size of the adult animal. The shell is now (see Pl. VIII, 

 fig. 1) as large as fully to admit of the animal withdrawing itself 

 with in the cavity. It exhibits an oval form, the dorsal edge 

 being still almost straight and the umbones very little if at all 

 projecting. Moreover, the shell is without any trace of the con- 

 centric lines of growth distinguishing the shell of the adult ani- 

 mal. These lines appear successively during the further growth 

 of the animal, at first but one, then two (see fig. 4), and so on 

 to seven, which number would appear to be the maximum. 



As may be seen from the above-given description of the 

 various stages, the development of the present Phyllopod is 

 wholly unlike that observed in other forms of this suborder, 

 being quite direct and successive, without any metamorphosis, 

 much as in the Cladocera. In [all other known Phyllopoda, with- 

 out exception, the young hatched from the ova are small free 

 Nauplii, which pass through a series of metamorphoses before 

 attaining their final developement, This is stated to be the case 



