194 PROFESSOR HUXLEY ON THE ANATOMY 
Pyrosoines, et sur la place qu'ils doivent occuper dans une classification naturelle*," and 
showed that Lamarck was in error in assigning to Tyrosoma a place near Beroe\ the 
animal being, in reality, a mollusk closely allied to Salpa {I. c. p. 420) „ 
The species described by Lesuenr was named by him P. giganteum, and was obtained 
in the Mediterranean, near Nice. 
Tyrosoma giganteum, says Lesnenr, has the general form common to the two other 
species ; it is transparent, of a starchy blue colour, soft and gelatinous, though slightly 
coriaceous; its only aperture, placed at the upper end, is bounded by tubercles and 
provided with a membranous expansion, which in certain cases serves to close it. The 
whole body is covered externally with tubercles, but these are not disposed regularly 
like those of Pyrosoma elegans ; they vary in their dimensions, some being short and 
indistinct, while others are greatly developed. The largest are conico- cylindrical, flat- 
tened and lanceolate at the extremity (while those of P. atlcmticum are simply conical), 
with a small aperture situated upon that side which looks towards the bottom of the sac : 
this lanceolate extremity is notched on its sharp edges, and presents below, between its 
pointed extremity and the opening of which we have just spoken, a small but very pro- 
minent keel. The inner surface of the Tyrosoma is smooth, and provided with a great 
quantity of little apertures, each of which corresponds with one of the tubercles, and is 
only the anterior end of a canal, whose posterior aperture is placed at the free extremity 
of the tubercle, — a fact easily demonstrated by pouring water into the sac-like body of 
the Tyrosoma ; for the water passes out immediately, in a multitude of distinct jets, 
from the extremities of the tubercles. 
Lesueur next proceeds to describe the internal structure of the Tyrosoma. He men- 
tions the internal and atrial tunics as one internal tunic, and points out their distinctness 
from the external, except at the aperture and over those rounded lateral bodies, which I 
have much reason to think are renal organs. The branchial networks are recognized as 
such ; the endostyle is described as " un vaisseau replie sur lui-meme ;" the testis is noted, 
but is interpreted as the liver. The stomach is determined as such, while the intestine is 
regarded as the oesophagus ; and the oesophagus is considered to be the pylorus, opening 
into what Lesueur regards as the intestine—" un canal assez large, glanduleux vers sa 
base " (p. 417), but which is, in reality, a sinus full of blood-corpuscles. 
The peripharyngeal ridge is accurately described as " deux petits filets qui vont en se 
courbant de chaque cote," &c. (p. 419) ; and the nature of the nervous ganglion is rightly 
determined. Tyrosoma is classed among the compound organisms, and the foetuses are 
carefully though briefly noted. Lesueur confirms Peron's statement concerning the 
rhythmical contractions exhibited by the whole body in the Fyrosomata. 
The figures which accompany this memoir are exceedingly good. I judge from them 
that Lesueur observed the atrial muscles, and that he has mentioned them as the line 
which separates the first zone of his transverse section (fig. 13 b) from the second (p. 415) ; 
and again, in the description of the figures 5 & 6, as " les filets qui forment un reseau dont 
l'usage parait etre de lier les animaux du Tyrosome entre eux." In n, fig. 5, I imagine 
for June of the same year. 
Journal 
