400 
Dr. 0. Burger on the 
in the first two groups is provided with nematocysts (we were 
able to determine the presence of rhabdites only), in the 
third , with the exception of the parasitic Malacobdella, it is 
armed with stylets. The proboscis varies in structure in 
Groups I. and II., and even in the arrangement of the layers 
of its wall we find important variations between a Eupolia 
and a Cerebratulus . The proboscis of Garinella is composed 
of a circular and a strong longitudinal muscle-layer, while 
that of Eupolia shows the opposite arrangement of a longi- 
tudinal and a circular layer. In Cerebratulus , again, we find 
that the proboscis repeats the structure of the musculature of 
the body-wall, and we get a longitudinal, a circular, and a 
longitudinal muscle-layer. In Carinella the nerves of the 
proboscis adjoin the circular muscle-layer, but in the case of 
Eupolia the longitudinal layer, and in this the nerve-tissue 
exhibits a condition which, so far as my own experience goes, 
is only repeated in the proboscis of the Enopla, viz. that the 
nerve-mass is not adjacent to a circular muscle-layer, as it other- 
wise is in all our species, be they those of Carinella , Eupolia , 
Cerebratulus , Drepanophorus , &c., wherever we find that the 
nerve-mass has a constant position, whether in the form of a 
nerve or of a nerve-sheath. In the proboscis of Cerebratulus 
the nervous plexus, derived from the expansion of the two 
nerve-cords, adjoins the circular muscle-layer on the inner 
side. The proboscis of the Enopla exhibits a precisely 
similar structure, consisting of circular, longitudinal, and 
circular layers. The nerve-cords are imbedded in the longi- 
tudinal muscle-layer, dividing it into two sheets. The aper- 
ture of the proboscis-sheath, however, is not, as has often been 
assumed to be the case, terminal in position ; on the contrary, 
it is in all forms subterminal and ventral. This is clearly 
expressed even in Carinella , where the tip of the head pro- 
jects beyond the aperture of the proboscis-sheath. Another 
organ, however, the cephalic gland, does open terminally to 
the exterior. 
A comparison has been suggested between the proboscis of 
Nemertines and the so-called proboscis of the Turbellaria 
Proboscidea, a terminally placed retractile and extensile 
sense-organ. Yves Delages * and Salensky t are among the 
more recent advocates of this theory. In opposition to this 
we may repeat once more that the aperture by which the 
Nemertine proboscis is extruded is by no means terminal, 
* Yves Delages, “ Etudes histologiques sur les Planaires Rhabdocoeles 
Acoeles,’’ Arch, de Zool. experiment, et gener. s6v. 2, t. iv. 1886. 
t Salensky, u Bau u. Metamorphose d. Pilidiums,” Zeitschr. fiir wiss. 
Zoologie, Bd. xliii. 1886. 
