Dr. R. Greeff on Autolytus prolifer. 181 
_ The specific characters* of Awtolytus prolifer are in many 
respects difficult to fix; thus, as a matter of course, we must 
give up even an approximate determination of the length or 
number of segments of the primary individuals, since these 
characters, as may be easily seen, vary greatly in consequence 
of prolification. The smallest primary individual engaged 
in prolification, observed by me, measured 2 millims. to the 
youngest bud offspring, and contained to the same point four- 
teen segments, with the exception of the head. The largest 
primary animal engaged in prolification, on the other hand, 
measured more than twice as much as the former, and con- 
tained thirty-nine segments to the commencement of the bud 
offspring. The fully developed animal before the commence- 
ment of prolification must therefore have been a good deal 
longer. I think, however, that the length of Autolytus pro- 
we will not usually much exceed 2 lines, as stated also by 
ohn. 
The head presents no indication of lobe-formation on its 
upper surface; but on the lower surface there is a narrow, 
median, longitudinal, impressed line, which divides and widens 
in a curve to right and left posteriorly, and thus forms the 
anterior buccal angle, so that the hinder parts of the head- 
lobes at the same time form the anterior buccal lobes or 
lips. _ Directly opposite to this anterior buccal angle there is 
a posterior one, the arms of which join those of the anterior 
angle, so that by this means a lateral angle is also pro- 
duced on each side. The buccal orifice has a quadrangular 
form, bounded by curved lines with their convexity in- 
wards. On its upper surface the head bears four reddish- 
brown eyes, furnished with lenses, the position of which, 
however, varies according as the two on each side are more or 
less approximated to or removed from each other, as shown 
in our figures. Usually they group themselves in a quadran- 
gle, the anterior pair being further apart than the second (pos- 
terior) pair. The three cephalic tentacles occur of very different 
sizes in different individuals; generally, however, they do not 
attain the very considerable length represented in fig. 1, but 
are much shorter. They are then capable of very lively move- 
ment, are constantly waved to and fro, and pushed through 
each other, feeling about, and, when thus employed, show the 
peculiar transversely furrowed and twisted appearance already 
* I shall refer only to the specific characters of the primary individuals 
of Autolytus prolifer, as good and perfectly satisfactory descriptions of the 
male and female bud offspring (Sacconereis and Polybostrichus) have been 
a by the authors already cited, and to these I can add nothing essen~ 
tial. 3 
