MUSEUM OF COMPARATIVE ZOOLOGY. 325 



unites with the outer tunic, and the external atrial opening is formed 

 by absorption. See Figs 1, 24, 25; 3, 38, and 34, g* 



The Heart. — I was prevented, by lack of time, from making a. 

 btiies of observations upon the manner in which the heart originates, 

 and accordingly quote what Leuckart (p. 55) gives upon this subject : 

 " The heart presents, at the earliest stages, an oval form, and lies in 

 the space between the nucleus and the ventral surface above the 

 placenta." See Fig. 24, k, of the present paper. " One end is di- 

 rected obliquely upward and backward, and the other forward and 

 downward. At first, as already stated, it is a solid mass of cells, with- 

 in which a cavity gradually appears [according to Vogt, p. 84, the 

 heart is hollow from the first] and thus becomes transformed into a 

 pouch, whose walls quickly become thin, and also, very early exhibits 

 a pericardium. The first faint pulsations are separated from each 

 other by long intervals, but are to be seen at a. period when the ends 

 of the heart seem to be closed. A circulation becomes visible only 

 after most of the other organs are formed ; but as the blood contains 

 no globules during the earliest stages, the absence of a circulation 

 cannot be absolutely affirmed." 



The Nervous System. — The ganglion, when first observed (Fig. 22, 

 v), was a hollow oval chamber, with indications of an opening at 

 the anterior end. As it was impossible to devote much time to the 



* Most of the writers upon Salpahave entirely mistaken the nature of the branchial 

 sac, and its relation to the typical form among the Tunicata, and Leuckart seems to be 

 the only one who has recognized the fact that the so-called "gill" is simply the sinus 

 between two large branchial slits. His statement is clear, and, as far as it goes, cor- 

 rect. He says (p. 56) : "Kurz nach der Aushohlung der Ganglionkapsel beobachtet 

 man in der Riickenwand des Embryos eine neue Bildung. (Tab. 11, Fig. 6.) Es 

 entsteht hier in der Mitte, zwichen der Ganglionkapsel und der Wurzel des Nucleus 

 wie fruher im Innern des Embryonalkorpers, eine lichte Stelle, die sich allmahlig'in 

 einen langlichcn Hohlraum verwandelt, und jederseits durch die Wand der Athem- 

 hohle hindurchbricht. Die Innenlage der Riickenwand, die Anfangs beide Hohlen von 

 einander trennte, wird durch diesen Durchbruch in einen cylindrischen Strang verwan- 

 delt, der von der Wurzel des Nucleus nach dem spatern Nervenknoten hinzieht, und 

 naturlicher Weise nichts Anderes, als die erste Anlage der Kieme sein kann. Die 

 Hohle durch welche die Kieme von der Kurperwand abgetrennt wird, ist die Kloak- 

 hohle, die also auch bei den Salpen, als ein eigncr, von der Athemhohle (im engeren 

 Sinne) verschiedener Hohlraum ihren Ursprung nimmt." 



As far as this goes it is correct, but he makes no mention of a special tunic around 

 the cloacal chamber, and says nothing of the lateral atria, or of the origin of the mus- 

 cular bands. 



