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name of the " segmental organ*" In the chambers which are 

 enclosed by the vertical dissepiments dividing the body of Actinia, 

 convoluted tubular cords are contained which support the genera- 

 tive structures. It has not yet been proved whether the internal 

 ends of these tubules open directly into the perivisceral chamber. 

 These cords and their appended structures in the Actiniadse, consti- 

 tute the type of a system of organs the prevalence of which through- 

 out the Echinodermata, Rotifera and Annelida can, he believes, be 

 clearly and satisfactorily proved. In the present memoir, however, 

 the author proposes to confine his demonstrations to the anatomical 

 varieties which the segmental organ presents in the class Annelida, 

 contenting himself with merely in a passing manner pointing out the 

 fact that the several variations of form, structure and number which 

 this organ exhibits in the several genera of this class, are represented 

 by similar variations in the different genera, especially of the class 

 Echinodermata. He hoped to show that under very numerous appa- 

 rent varieties, the essential unity of the segmental organ within the 

 indicated limits can be convincingly established. 



Upon this organ, under different circumstances, there devolve one 

 or two or even more functions. Sometimes it is used as a simple 

 discharge tube, conveying externally in a direct manner the fluid of 

 the general cavity of the body. This variety is exemplified in the 

 segmental organs which are distributed, in the genera Lumbricus 

 and Nais, throughout all that part of the body which is situated 

 posterior to the Reproductive band. In this latter region two or 

 more of these organs are so modified as to become the basis whereon 

 is developed the generative structures. 



Here the author enters upon a minute account (illustrated by 

 figures) of the history of this organ in Lumbricus and Nais, showing 

 the changes of outward form which it undergoes in several species of 

 these genera. 



He points out in this place that the segmental organ, as it occurs 

 in Lumbricus and Nais, is paralleled by the so-called water-vascular 

 system of the Rotifera : as in the former so in the latter, the ciliated 

 tubes communicate openly with the general cavity ; in both, the cur- 



* While he is convinced that the identity of this organ might readily be traced 

 throughout other families of the lower Invertebrata, he will not permit himself at 

 present to indulge in any wider generalization than that stated in the text. 



