402 
Dr. 0. Burger on the 
and a section of the dorsal blood-vessel. This constitutes the 
u 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 (blastocoele) . 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 Prosadenoporus , 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 csecal 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 Valencinia , Eupolia , Amphiporus 
lactifloreus , &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 Nephridial Apparatus of the 
Nemertea,” Q. J. M. S. vol. xix. n. s. 1885. 
t Silliman, “ Beobaehtung dber Susswasserturbellarien Nordamerikas,” 
Zeitschr. fiir wiss. Zoologie, Bd. xli. 1885. 
