DE. M'INTOSH Olir BRITISH SALP^. 47 



The solitary form of S. spinosa is very transparent, and during 

 life its six circular muscular bundles are also only seen as faint 

 lines during contraction. In addition to the characteristic pos- 

 terior spines, there is a stout bifid spinous process {g, figs 5 & 6) 

 and a small lateral spine on each side of the coiled chain. A 

 small red ocellus is seen at a, fig. 5, and four opake dots at h. 

 The branchiae, endostyle, nucleus, and coiled chain with various 

 grades of developing youug are represented in the figures. After 

 preservation in spirit the inner tunic is seen to end, in each of 

 the long posterior spines, in a trumpet-shaped process. This ap- 

 pearance is also observed in figs. 7 and 8, vphich represent a front 

 and lateral view of a small and very active individual captured 

 with the towing-net. It is probably a developing specimen of 

 this form, judging from the number of muscular bundles and the 

 trumpet-shaped ending of the tunic in the posterior processes. 

 The latter, however, are flattened, oar-shaped, and short. It also 

 possessed the bifid spinous process, at h, fig. 7. The nucleus was 

 of a dull white hue in life ; and the embryonic body, a, was still 

 present. In one case the adult solitary form of this species was 

 dead, as likewise were the included young; but the individuals 

 (measuring y^th of an inch long) of the pigmy chain depending 

 from the parent contracted vigorously. Each was furnished with 

 a little red ocellus. 



The individuals of the aggregate form of >S^. spinosa were of all 

 sizes, from f of an inch in diameter downwards. Their figure was 

 somewhat pyriform and facetted (fig. 9). The nucleus is tinted 

 of a fine bluish purple with a streak of yellow, and the branchial 

 apparatus has also the former hue. At the anterior end of the 

 nucleus a constant ciliary motion was seen under the lens,, not 

 connected with the eflerent current issuing at the posterior 

 aperture. "When adhering together in chains, they swim with 

 the bluish-purple nucleus downwards ; and the same remarks ap- 

 ply to their mode of locomotion as to the ribands of S. runcinata. 

 The chains of the former were in general much shorter than those 

 of the latter, though broader in proportion, since they were com- 

 posed of a double row with the individuals arranged alternately ; 

 that is, the transverse fissures of the one row were opposite the 

 centres of the other. 



"When swimming in a vessel during the day, the contractions of 

 Salpa spinosa and its aberrant form caused a lens-like conden- 

 sation of the rays of light, which flashed on the glass beneath 

 them on each occasion. S. rtmcinata was not observed to be lu- 



