258 Jl monograph of the Australian aphroditea, 



Aphrodltea witli their homologues in the typical Annelids. In 

 the absence of proof, however, upon this point, they must be 

 described as commencing in a single tube, the internal extremity 

 of which divides into a numerous system of branches. None of 

 these branches communicate openly with the cavity of the body." 



I have not had the apportunity of dissecting any fresh or well- 

 preserved specimens of Aphrodiia, but the above account is stated 

 by Williams to apply also to the arrangement of the segmental 

 organs in Pohjnoe, and I find the arrangement in that genus so 

 totally different from that described by AVilliams, that I have 

 been led to an explanation of Williams's observations and figures 

 which at least reconciles them with what I find to exist in those 

 PoIyyioidcE in which I have worked out this point. In the first 

 place it is to be noted that Williams gives no clue to the position 

 of the external orifice ; he admits in fact that he had not been 

 able to follow the canal through the integuments. In the second 

 place, in the figure which he gives of the alimentary canal and 

 supposed segmental organs in Aphrodiia (I.e., j)l. viii., fig. 26) he 

 either has omitted altogether a portion of each intestinal ceecum, 

 or, as I incline to believe, has represented it as the segmental 

 organ. In the third place the figures which he gives of the 

 segmental organ (fig. 27) of Fohjnoe resemble very closely the 

 intestinal caeca in some species of that family when invested by 

 the developing ova, and the position of the orifices relatively to 

 one another and to the middle line answers very Avell to the 

 position of the apertures of communication of the ca)ca with the 

 intestine. Further it has to be observed that, were AVilliams' s 

 account to be accepted, we should be obliged to admit that the 

 segmental organs and sexual glands of Aphrodita and Folyno'c 

 are framed on a type totally unlike that observed in any other 

 Annelide ; he represents the former as complexly branched tubes, 

 not opening into the perivisceral cavity, but opening externally, 

 and the latter as being situated in the interior of the former ; 

 whoroas in other Annolidcs the segmoutul organs are uubranchod, 



