ON THE BRITISH ANNELIDA. 245 



Having arrived in the chamber of this great caecum, it will of course follow 

 on the same ground, that the refuse matter can only escape by the same me- 

 chanism, for no direct outlet to this cavity can anywhere be discovered. It 

 is therefore a perfectly closed sac, filled with a milky fluid. But it must not 

 be overlooked that its interior cavity is considerably multiplied by the super- 

 addition o^ diverticula (fig. 64 e, i) to the sides. The parietes of these last parts 

 are more glandular, granular and darker than those of the ventral or dorsal 

 aspect of the tube. This granular character has been invariably misconstrued 

 by every observer into an evidence of the ovarian signification of these parts. 

 The microscope places the inaccuracy of this view beyond dispute by demon- 

 strating that these ova (otc) consist only of oil-globules. 



This organ is tied at definite intervals, by means of minute bridles, to the 

 integument, according to the manner in which, in nearly all Annelida, the in- 

 testine is connected with the cylinder of the integument, ^t its posterior, 

 caudal termination it has been proved, by repeated observations, that there 

 exists no orifice; of this fact there is no doubt. It is then proved by direct 

 demonstration that there is neither an inlet nor an outlet to this remarkable 

 organ, and it is hoped that evidence has been accumulated to superfluity, to 

 establish its digestive character. But through another line of inquiry these 

 proofs receive additional force. At short distances, along the whole line of 

 the body of these worms on either side, membranous sacculi may be defined 

 with readiness in the interval between the alimentary tube and that of the 

 integument. It is on these organs undoubtedly that the office of reproduction 

 devolves. If this be not their true function, no other can be assigned to them; 

 and if this be their real meaning, it follows that no other than that of digestion 

 remains for that organ, which the author has ventured to designate as the 

 great alimentary cmcum*. 



The key to the real organization of this unfamiliar group of Annelids 

 having thus been forged by the demonstration of the structure of a few 

 typical and illustrative species, material assistance is aff'orded for unlocking 

 the difficult anatomy of all the allied genera. Taking for groundwork the 

 plan on which the Planarice are formed, the anatomist may trace the indica- 

 tions of the same constructional pi'inciple from the genus Litieus, through 

 that oiBorlasia, Gordius, Meckelia, Serpentaria and Prostoma, genera which 

 are characterized by the possession of a long proboscis and short oesophagus, 

 forming a system almost distinct from the great digestive ccecum. In passing 

 to the Planarice, these two prehensile structures disappear, and the mouth 

 opens directly, without any intermediate tubular arrangement, into the di- 

 gestive cavity. The caecal ramifications of the digestive system of the Pla- 

 narice are the precise equivalents of the great digestive ccecum with its se- 

 condary diverticula, as observed in the Nemertinida:. 



The anatomy of the Planarice conveys an exact expression, in all its de- 

 tails, of that of the parenchymatous Entozoa. The digestive apparatus of the 

 genera Fasciola and Distoma is conformable to the same type. Like the 



* As it would be out of order to enter in this place into a detailed description of the re- 

 productive organs of these wpnns, no further proof can be adduced, bearing upon the ques- 

 tion of the digestive character of the organ which in the text I have denominated " the great 

 digestive caecum." In the second part of this Report, vphich I trust will appear in the next 

 year's Volume of the Transactions, some further observations on the reproductive organs will 

 be added in connexion with the subject of the Embryology of the Annelida. At present I 

 ■ only desire to indicate the example of the Planarian family, as sufficient to prove that in 

 them at least, the digestive cseca, so exactly homologous with the alimentary caecum of the 

 Nemertinidrs, have been shovra incontestably to be wholly unconnected with, and indepen- 

 dent of, the reproductive system, the anatomy of which, in aU its minutest details, may be 

 defined vrith perfect clearness. 



