1896. ] PLANKTON OF THE FAEROE OHANNEL. 995 
form, mouth dorsal, cloaca terminal. Surface smooth. Length of 
sexual form 12 mm. 
Tsr clear, transparent, thin. 
Mantiz.—In the sexual form the musculature exhibits an 
asymmetry similar to that already described in S. dolichosoma- 
virgula, musculosa-punctata, and magalhanica*. The mouth has a 
pair of sphincters, apparently formed by splitting of two lateral 
longitudinal muscle-slips. At least one sphincter surrounds the 
cloacal aperture ; but the arrangement of the musculature of both 
apertures was extremely difficult to make out, owing to the bad 
condition of the specimens. The order, or rather the disorder, of 
the main muscles is more easily appreciated from drawings than 
from a description (Plate L. figs. 5, 6,a—f). In addition to these 
there are two dorsal longitudinal muscle-slips, a dorsal sheet 
overlying the nucleus, and a fan-like sheet on the right of the 
nucleus. 
In the solitary form, extracted with the placenta from the 
parent, the musculature is much more regular; it consists of 
eight complete bands, two large and (?) four small circumcloacal 
sphincters (the arrangement of which could not be exactly ascer- 
tained), a right and a left longitudinal slip of unequal length in 
connection with the two circumoral sphincters. 
Enpostyzs fairly long and straight. 
Dorsat Lamina large (diam. in posterior third about 5 mm. in 
sexual form), with strongly-marked ridges. No languet was 
detected. 
Dorsal TUBERCLE large, about 5 mm. in length in sexual form 5 
transversely marked with fine bands of cells. 
ViscCERAL Mass comparatively small, brownish yellow in life. 
At first it seemed probable that one was dealing merely with a 
specimen curiously broken, and that the asymmetry was artificial. 
But specimens of this species were taken on many occasions, and 
all possibility of the above explanation was destroyed when I 
obtained several specimens which presented the same asymmetry, 
but in a “ Spiegelbild,” namely the reversal which would be pro- 
duced by a reflection in a mirror. The same reversal or “ inverse 
image” has been discussed at length by Apstein * on the basis of 
the three asymmetrical genera cited above. 
As the ‘Ergebnisse der Plankton Expedition’ are not readily 
accessible to everyone, and as the point is novel and of some 
interest, I quote Apstein’s conclusions :—“ Bei den iibrigen Salpen, 
die eine symmetrische Muskulatur haben, ist Spiegelbild und 
Kongruenz dasselbe, bei einem unsymmetrischen K6rper aber fallen 
Spiegelbild und Kongruenz nicht zusammen. Ich glaube jedoch, 
dass bei allen Salpen in der Kette die Individuen der eine Reihe 
gleich, d. h. kongruent sind, aber zu denen der anderer Reihe 
spiegelbildlich sich verhalten, aber dass dies in der Muskulatur 
1 Apstein, ‘Ergebnisse der Plankton Expedition: Die Thaliacea.—B. Ver- 
teilung der Salpen,’ p. 17. 
2 Apstein, loc. cit. p. 17. 
