396' Royal Society .— 



seated on separate individuals ; that the reproductive elements at no 

 time find their way into the general cavity ; that in fact these Anne- 

 lids, anomalous only in the disposition of their alimentary system, 

 conform, as regards the type and mode of repetition of segmental 

 organs, to the standard offered by the great Nereid group. 



Chlorcema Bvjardinii, especially the female, presents an extremely 

 favourable opportunity of observing the looped arrangement of the 

 segmental organ, and of proving the fact, so constantly seen in the 

 other families of Annelids, viz. that one limb of the loop is the true 

 ovary, or the primary seat of the ovo-genesis ; that the ovules travel 

 round the curve of the loop ; that they acquire a considerably deve- 

 loped size at the other limb, just before they escape externally. In 

 Chlorcema the vitelline body of the ova is almost ink-black. The 

 entire extent of the segmental organ is thus rendered perfectly and 

 easily traceable amid the surrounding transparent structures. In this 

 genus it does not at present appear that either limb of the loop opens 

 into the general cavity. This type prevails, as far as he knows at 

 present, throughout the Nereid group ; in other words, in these An- 

 nelids the function of a discharge tube does not appear to be thrown 

 upon the segmental organ under any circumstances ; hence the limited 

 dimensions of the general cavity and the highly developed character 

 of the blood- vascular apparatus. 



The group lastly examined is that of the Aphroditacese. On the 

 reproductive organs of this large, numerous and interesting family, 

 no single observation is contained in any work on comparative ana- 

 tomy that the author is acquainted with. He enters upon a detailed 

 account of his own researches. They have ended in what he would 

 fain believe to be a complete solution of the difficulties in which the 

 history of the Reproductive or segmental system of this family has 

 been hitherto shrouded. This family, without exception, is uni- 

 sexual. The segmental organs constitute a complete and regularly 

 branched series, situated, as in all other Annelids, on either side of 

 the ventral median line. They embrace, like a gauze-work, the 

 diverticula of the alimentary system, with which they correspond in 

 number. They fall under the general designation of the *' segmental 

 organ," in the feature of their having two limbs, being therefore 

 looped, although only rudimentarily. The author then proceeds to 

 give an account of his studies into the history of this organ amongst 

 the grotesque and highly varied species of the genus Polynoe. They 

 have rendered it certain that throughout the family of the Aphro- 

 ditaceae there obtains but one type of segmental organ, and that 

 upon it always are ingrafted the generative structures. 



At this stage the attempt is made to show that the segmental 

 organs of the Echinidae, Asteriadse and Ilolothuriadse conform, 

 structurally and functionally, in the most remarkably intimate man- 

 ner with the typical standard exhibited by this organ in the Aphro- 

 ditacese. But between these Echinoderm and Annelidan families the 

 author attempts to indicate other zoological affinities. He shows, 

 that, according to his researches amongst the Aphroditacea3, there is 

 no trace whatever to be discovered of a blood-vascular system. In 



