1896.] PIANKTON OF THE FABEOB OHA.NNHL. 995 



form, mouth dorsal, cloaca terminal. Surface smooth. Length of 

 sexual form 12 mm. 



Test clear, transparent, thin. 



Mantle. — In the sexual form the musculature exhibits an 

 asymmetry similar to that already described in 8. dolicliosoma- 

 viryula, musculosa-jpunciata, 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 malie out, owing to the bad 

 condition of the specimens. The order, or rather the disorder, of 

 the main muscles is more easily apjireciated from drawings than 

 from a description (Plate L. figs. 5, 6, a-f). In addition to these 

 there are two dorsal longitudinal muscle-shps, 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. 



Endostxlb fairly long and straight. 



DoESAL LAMINA large (diam. in posterior third about 5 mm. in 

 sexual form), with strongly-marked ridges. No languefc was 

 detected. 



DoESAL TUBERCLE large, about 5 mm. in length in sexual form? 

 transversely marked with fine bands of cells. 



ViscEEAL 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 w'as 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 ' Brgebnisse 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 Korper aber fallen 

 Spiegelbild und Kongruenz niclit zusammen. Ich glaube jedocb, 

 dass bei alien Salpen in der Kette die Individuen der eine lleihe 

 gleich, d. h. kongruent sind, aber zu denen der anderer Eeihe 

 spiegelbildlich sich verhalten, aber dass dies in der Muskulatur 



' Apstein, ' Ergebnisse der Plankton Expedition : Die Thaliacea. — B. Ver- 

 teilung der Salpen,' p. 17. 

 " Apstein, loo. cit, p. 17. 



