ON THE BRITISH ANNELIDA. 243 



the 90-calIed ovarium is rendered not the less probable. It will afterwards 

 become apparent that two distinct lines of inquiry converge upon the infer- 

 ence that this " ovarium " of authors is a true digestive caecum on a large 

 scale; that it is filled by a chylous fluid, charged with organized corpuscles ; 

 that its parietes are organized with especial view to supply a secretion by 

 which the fluid contents are assimilated ; and that the whole force of analogical 

 inquiry supports the view which assigns to other structures exterior to, and 

 independent of this organ, the functions of reproduction. It is proposed at 

 this place to enter into the details of the demonstrations which the author 

 has to ofler with reference to the anatomy of the genera Borlasia, Linens 

 and Gordius. The grounds will then become intelligible on which he enter- 

 tains the belief that the principles of structures developed by these researches, 

 when extended to the instances of the cestoid Entozoa, will prove no less 

 exact. 



The whole exterior of the body in these worms is one continued scene of 

 ciliary vibration. This extraordinary fact it is essential to remember, since 

 it will be found to bear corroboratively on the views afterwards to be ex- 

 plained, as to the uses of structures hitherto held as enigmatical*. At a 

 point a little posterior to the extreme end of the rostrum, and corresponding 

 with what CErsted has designated Jissurce respiratorice laterales, the cilia 

 assume an augmented size, appearing in this situation as though supplied to 

 guard fissural openings leading into cavities. These apparent openings are 

 really only depressions, spaces left between the cervical muscles, in order to 

 make room for the heart, which is situated on each side immediately under- 

 neath, to expand. The red colour of these two spots on either cheek is due 

 to the blood in the heart, which (Plate XI. fig. 64a, a) is a bilocular organ. 

 The blood colour of these spots has led nearly all observers to the mistake 

 of supposing that the office of respiration is circumscribed to these limited fis- 

 sures. The microscope, which resolves the part into its component elements, 

 furnishes a direct disproof to this view. In structures devoted to respiration, 

 the blood is uniformly divided and subdivided into the minutest streams. 

 In this part this fundamental law is violated, for here the blood is accumu- 

 lated into one large cardiac chamber. In these Annelids the proboscidean 

 orifice is not terminally but ventrally situated. It is slightly behind and on 

 the abdominal surface of the conical snout which forms the cephalic termi- 

 nation of the body. In itself this opening is a simple longitudinal slit, adapted 

 for no me*chanical purpose. Its sides are smooth, and armed with no mecha- 

 nical instruments. It is merely an opening through which, in Borlasia, 

 Lineus and Gordius, a powerful and an extremely long proboscis is pro- 

 truded (fig. 64 B). The extremity of this organ is armed with several sty- 

 leted jaws (fig. 64 c), which, from their construction, seem designed only to 

 fix the suctorial end, h^ perforating the alimentary object. When the pro- 

 boscis is withdrawn into the interior of the body, fitting admirably into a 



and Gordius, the anatomy of which my dissections, I trust, have reduced to clear demonstra. 

 tion, the ' alimentary organ,' the great digestive caecum, which both in general and ultimate 

 structure is the exact counterpart of what is called in TeBnia " the ovary," has been proved 

 beyond dispute to have no direct external communication. Its contents, therefore, which 

 the microscope demonstrates to consist of an organized corpusculated fluid, of a milky 

 character (the correlate of that which in other Entozoaand Annelida occupies the jBenYowea/ 

 chamber, i.e. exterior to the aUmentary organ), cannot be excrementitious ; it is chylous. 

 It is the pabulum which in part supplies the materials out of which the blood-proper is formed, 

 and by which, in part probably, the work of solid organization is accomplished. 



* I have not yet succeeded in actually proving the existence of cilia on the integuments 

 of Gordius ; from the resemblance of its internal structiu-e, however, to that of the Liniadm, 

 of which the cutaneous surface is richly ciliated, it is scarcely rash to believe that in it also 

 these motive organules will be found to exist. 



r2 



