194 PROFESSOR HUXLEY ON THE ANATOMY 



Pyrosomes, et sur la place qu'ils doiveut occuper dans une classification naturelle*," and 

 showed that Lamarck was in error in assigning to JPyrosoma a place near Beroe, the 

 animal being, in reality, a mollusk closely allied to Salpa {I. c. p. 420). 



The species described by Lesueur was named by him F. giganteum, and was obtained 

 in the Mediterranean, near Nice. 



JPyrosoma giganteum, says Lesuenr, has the general form common to the two other 

 species ; it is transparent, of a starchy blue colom', 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 tiibercles, but these are not disposed regularly 

 like those of Pyrosoma elegcms ; 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. atlmiticum 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 Pyrosoma is smooth, and provided with a great 

 qiiantity of little apertures, each of which corresponds with one of the tubercles, and is 

 only the anterior end of a canal, whoso 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 Pyrosoma; 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 Pyrosoma. 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 c6t6," &c. (p, 419) ; and the nature of the nervous ganglion is rightly 

 determined. Pyrosoma is classed among the compound organisms, and the foetuses are 

 carefully though briefly noted. Lesueur confirms P^ron's statement concerning the 

 rhythmical contractions exhibited by the whole body in the Pyrosomata. 



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 h) from the second (p. 415) ; 

 and again, in the description of the figures 5 & 6, as " les filets qui forment un reseau dont 

 I'usage parait etre de lier les auimaux du Pyrosome entre eux." In n, fig. 5, I imagine 



* Read to the Socicte Philomatique de Paria on the 4th of March, 181.5, and published in the ' Journal de Physique * 

 for June of the same year. 



