102 



TUNICATA. 



divided into thorax, abdomen, and postabdomen. The heart lies at the hind 

 end of the body. Amarcecium Edw. ; A proliferum Edw. 



Order 4. ASCIDI^E SALP.EFORMES.* 



Free-swimming colonies, which float on the surface of the sea, and 

 have in general the form of a fir cone, hollowed out like a thimble. 

 They are composed of numerous individuals arranged in the common 

 gelatine-cartilaginous mass in a direction at right angles to the long 

 axis of the colony. The inhalent openings lie in irregular circles on 

 the external surface ; the exhalent openings open opposite to them 

 into the space which serves as a common cloaca. The branchial sac 

 is wide and latticed as in the Ascidians. The intestine and ovary are 

 compressed together, and lie in a rounded prominence like a nucleus 



N 



Ki 



Wb 



FIG. 565. An individual of Pyrcsoma, (after Keferstein). 0, Mouth ; A, atrial aperture 

 Af, anus ; Ov, ovary ; T, te&t;s ; ^V, ganglion ; End, endoetyle ; Br, branchial sac ; Wb, arch 

 of cilia ; C, heart ; St, stolo prolifer. b, Cvathozoid of Pyrosoma (after Kowalevcki). 

 H, Heart ; Kl, cloaca ; D, yolk around which are the four individuals (ascidiozoids). 



(fig. 565 a) ; near them is the heart. The ovary brings only one 

 ovum to maturity, which is surrounded by a saccular follicle with a 

 long stalk. The stalk constitutes the oviduct, and opens into the 

 cloacal cavity. The eye lies on the ganglion. By the presence of 

 the eye, as well as by the position of the two respiratory openings 

 and of the viscera, by the method of reproduction and the free 

 locomotion, the Pyrosomidce are allied to the Salps. 



Budding takes place by means of a stolon, which begins at the 

 hind end of the endostyle, and contains an endodermal process of 



* Th. Huxley, " Anatomy and development of Pyrosoma." Trans. Linn. Soc., 

 1860. 



W. Keferstein tmd Ehlers. " Zpologische Beitrage." Leipzig. 1861. 



Kowalevski, " TTeber die Entwickelungsgeschichte der Pyrosomen." Arch, fur 

 mikr, Anatomic, Tom. XI., 1875. 



