402 Dr. 0. Burger on the 



and a section of the dorsal blood-vessel. This constitutes the 

 " rhynchocoelom," the wall of which similarly repeats the 

 structure of the body-wall, that is, of the muscular portion 

 thereof. The free corpuscles in the rhynchocoelom are to be 

 compared with those of the perivisceral fluid. 



We find therefore that the body of the more highly 

 organized Nemertines possesses two cavities, which we may 

 regard as constituting a body-cavity — the rhynchocoelom, or 

 cavity of the proboscis-sheath, and the cleft between the intes- 

 tine and the parenchyma. It must not be supposed that both 

 these spaces are of equal value. The cellular lining of the cleft, 

 which is in the highest degree similar to that of the genital sacs, 

 renders it extremely probable that this cavity is a schizocoel. 

 The rhynchocoelom, on the contrary, is a persistent segmen- 

 tation-cavity (blastoccele) . I must leave it to embryology to 

 say whether one or other of these cavities is homologous 

 with the body-cavity of the Annelids. 



The blood- vascular system attains its highest development 

 in Groups I. and II. as far as regards the elaboration of the 

 vessels ; in these groups we find, in addition to two or three 

 longitudinal trunks, which are united together in the head 

 and in the caudal extremity, an oesophageal blood-vascular 

 plexus, and behind this another surrounding the cavity of the 

 proboscis-sheath. Besides this we generally get in the second 

 group sinus-like blood-spaces for the cephalic pits. In the 

 three longitudinal vessels of the third group, which are united 

 to one another by a series of metamerically arranged trans- 

 verse loops, we have the nearest approach to the blood- 

 vascular system of the higher Annelids. A blood-vascular 

 system is wanting in the Turbellaria. 



A water-vascular system is probably present in all Nemer- 

 tines, with the exception of the terrestrial forms and the 

 genus ProsadefioporuSy in which I was not able to determine 

 it. That of Group I. is stated to open directly into the 

 blood-vessel. Be that as it may, it sends out caecal tubes 

 which enter and pierce the wall of the vessel. Most Nemer- 

 tines possess only a single pair of nephridial pores ; but in 

 many forms, including Valencim'a, Eupoliay Amphiporus 

 lactijioreus, &c., it is stated by Oudemans * that there are a 

 large number. 



The similarity between the excretory system of the Nemer- 

 tines and that of the Turbellarians is unmistakable, especially 

 if it should be more generally found, as Silliman f claims for 



* Oudemans, "The Circulatory and Nepliridial Apparatus of the 

 Nemertea," Q. J. M. S. vol. xix. Ta. s. 1886. 



t Silliman, " Beobachtung Liber Susswasserturbellarien Nordamerikas," 

 Zeitschr. fiir wiss. Zciologie, Bd. xli. 1885. 



