192 ON THE ANATOMY OF SAGITTA, 
in the contractile vegetable tissues. Trachelocera olor sud- 
denly contracts its neck and shortens itself; on a stronger 
current, it becomes fiattened out, sarcode escapes and the 
entire creature becomes diffluent, whilst exhibiting the weil- 
known wonderful contractions; the same thing takes place in 
Paramecium aurelia. 
Lastly, Hydra viridis exhibits exactly similar conditions. 
The outstretching of its tentacles, the elongation of the body, 
is manifestly an active proceeding. When at rest and after 
death, it becomes shortened into an almost invisible particle. 
In like manner, a weak induction-current causes an instanta- 
neous contraction of the body; under a continued current of 
the same strength, expansion gradually sets in again; a stronger 
current causes a renewed contraction ; a very powerful shock 
induces contraction to the utmost; but after this, expan- 
sion no longer takes place, but instead, a gradual dissolution 
of the body. 
The contractile phenomena in the parenehyma of plants 
and of the lower animals, consequently, so far as injury has 
as yet gone, follow the same laws. 
Notes on the Anatomy of SaGirta. 
Dr. H. A. Pacrnstecner* has described what he re- 
gards as a new species of Sagitta, occurring at Cette. But 
as, unfortunately, he appears to have met with only a single 
specimen, his determination of its specific distinction cannot 
be regarded as definitive. 
The specimen observed was furnished on one side with 
seven, and on the other with eight, large hooks. The 
smaller hooks were placed in two groups on either side, 
towards the middle of the under side of the upper hip. Hach 
group consisted of five pointed spines, all directed backwards. 
The two anterior groups were situated nearer to each other 
than the posterior. A bundle of the minute, bristle-like 
hairs, which have been observed on the sides of the body in 
other Sagitte, was in the present species noticed on each side, 
even of the head. The abdominal, anal, and caudal fins con- 
stituted a continuous expansion, surrounding the entire 
hinder part of the animal. The caudal portion of the Sagitta, 
though not more than 4 mm. long, was, nevertheless, filled 
* *Zeitsch, f. wiss. Zool,’ Bd, xii, p. 308, pl, xxix, fig. 8, 
