KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 39. N:o ll. 13 
KOREN and DANIELSSEN and by myself in the year 1875, though with different re- 
sults. The views of KOREN and DANIELSSEN are certainly wrong, though they seem 
nevertheless to have been accepted by SELENKA. 
The Tentacles. The arrangement of the tentacles -and their shape indubitably 
present good systematic characters; their number it may also in many cases be of a 
certain importance to know, though it is certainly not seldom of very little syste- 
matic value. The fact is, that the individual! variation in number is rather consider- 
able. To prove the truth of this, I need only refer to my descriptions of Phascolo- 
soma margaritaceum, Hansenii, procerum etc. Moreover, having had at my disposal, 
for the purposes of comparison, a splendid series of specimens of Ph. margaritaceum, 
I have been able to state the fact that the younger an individual is, the fewer are 
the tentacles. Unfortunately I never had the opportunity of studying any later develop- 
mental stages of our northern Gephyrea for the purposes of getting an insight into 
the growth of their tentacles. NSingularly enough, I must confess that I never 
happened to detect a single larva in all the thousand samples of Plancton, taken from 
the fjord of Gullmarn during the last thirty years, nor has, so far as I am aware, 
any other Swedish zoologist been successful in doing so. 
Several of the northern Gephyrea, e. g. Phascolosoma Sarsii, glaciale, Sabel- 
lariae, Onchnesoma Steenstruplii, are totally wanting in true tentacles, which are re- 
placed by a minute disk or fold, somewhat studded or buckled, surrounding the 
mouth. It is not likely that the tentacular disk of the animals enumerated repre- 
sents an original state, but rather a secondary, highly reduced, one. At any rate in 
Ph. Sabellariae, which 1s a true shallow-water form, it may be taken for granted 
that such is the case. Of course, a consequence of the disappearance of the ten- 
tacles has been a reduction, and at last a total disappearance, of the contractile vessel. 
Even it we leave it undecided as to whether the primitive forms of Gephyrea 
were provided with a simple tentacular disk or with a true compound crown, it does 
not seem difficult to derive the tentacle types of the Gephyrea from one or 
other of the two extremes. Starting from the simple disk, in order to explain the 
affinity of the other more compliecate tentacle types, I must expressly accentuate the 
fact that I abstain from pronouncing an opinion on the disposition of the primary 
tentacles in the original Gephyrea. 
Having had the opportunity of studying numbers of samples of several species, 
which in the adult state bear numerous tentaecles, I cam state that the younger a 
specimen is, the fewer are the tentacles. As the animal grows larger and the need 
of a vigorous respiration inereases, the respiratory surface must augment, and that 
takes place by means of an enlargement and folding over of the tentacular disk, to- 
gether with a continual increase in the number of the true tentacles. As a rule, 
the tentacles, arising from the more or less deeply folded rim of the disk, surround 
the mouth, forming a simple or compound crown round it. Supposing that the rim 
of the tentacular disk has become deeply folded, the tentacles which have protruded 
from it, assume the appearance of being arranged in several cireles and of forming 
a number of bundles or festoons. 
