KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 39. N:o |. id 
examined under a high magnifymg power, after treatment with the iron-hematoxylin 
of HEIDENHAIN each muscle-fibre is seen to display a series of broader and darker, 
transverse bands, separated by narrow light lines, indicating that a kind of differen- 
tiation of the contractile substance has taken place. Moreover, every fibre presents 
very fine longitudinal fibrille. But the above-mentioned "strie, visible in the con- 
tracted musecle, remain absent. 
How are we to interpret these two very different views of an unstriated mus- 
cular-cell? Supposing the muscular fibres to have been suitably isolated and stained, 
the matter is easy enough to understand. For it will be seen that every cell repre- 
sents an elongate, narrow, flattened fibre, which is transversely plaited and, further- 
more, turned in a spiral. In the state of contraction all the component plaits and 
coils are in close contact with one another, the fibre thus acquiring a transversely 
striped aspect; on the other hand, in the state of extension, the coils and plaits of 
the spiral fibre are remote one from the other. In order to illustrate the wohle 
arrangement by an example, one has only to cut a narrow slip of paper, 10 divide 
it into a number of folds and to turn it slightly spirally. It is evident that such a 
structural arrangement is very favourable for effecting a rapid and powerful move- 
ment. As far as I have been able to make out the muscular fibres of the retractors 
in several other groups of animals are also built up in a similar way. 
In this connection I may be allowed to treat a question of priority, of very 
little importance certainly, but nevertheless worth referring to. In his splendid work 
of the year 1883 SELENKA wrote: "Wie KOREN & DANIELSSEN zuerst bei Sipunculus 
(norvegicus und priapuloides) beobachteten, existirt zwischen der äusseren Ring- und 
inneren Längsmuskelschicht der Körperwand noch eine dritte diagonale Muskellage, 
welche jedoch im hinteren Körperabschnitte feh!t". In 1875, the same year that 
KOREN and DANIELSSEN published their preliminary account, I myself wrote, with 
regard to Phascolion strombi: "Si on examine plus attentivement les couches muscu- 
laires du Phascolion strombi, on trouve sans grande difficulté qu entre ces couches 
s'étend une quantité de bandelettes musculaires ténues qui ne semblent pas avoir été 
observées jusqw'å présent chez un seul Siponele. Ces bandelettes se trouvent séparées 
Pune de PFautre å peu pres å la méme distance; de plus, elles n'ont pas la méme 
direction que les filaments des sacs précédemment nommés, mais elles les coupent 
transversalement, de maniére å former des angles semi-droits avec eux. Les bande- 
lettes sont particulierement visibles å la portion antérieure du corps proprement dit.” 
SELENKA, with regard to the muscles in question, only refers to KOREN and DANIELSSEN 
of 1877, which proves that he did not know of, or perhaps was unable to read their 
earlier, preliminary, publication of 1875, which was published in the Norwegian lan- 
guage; yet that does not explain why he should have totally negleeted to mention 
my two papers of 1875, written in French and published both in Sweden and France, 
