"94 TUNICATA. 



Ascidians correspond to those of the Appendicularice, and consist of 

 the so-called endostyle with the ventral groove and the two ciliated 

 arches. 



The ciliated oesophagus is short and funnel-shaped, and leads into 

 a dilated portion distinguished as stomach, whose walls have a 

 layer of large entodermal cells and are complicated by the presence 

 of fold-like projections. Glands, which are sometimes follicular, 

 sometimes composed of bundles of tubes, or of tubes united in a 

 network, lie upon and open into the stomach ; they are generally 

 known as * liver, but would be better called hepatopancreas. The 

 small intestine which follows the stomach is of considerable length, 

 is usually bent on itself (haemal curvature), and is continued into a 

 short rectum (piriform in Appendicularia), which opens into the 

 cloacal chamber. Besides the glands already mentioned, a gland-like 

 organ has been found in many Ascidians : as there is no opening to 

 this gland, the concretions found in its lumen are probably not in 

 general removed. It may, perhaps, be regarded as a kidney, since 

 Kupffer f has shown that uric acid is present in the concretions. 



The heart is placed on the ventral side of the intestinal canal. 

 It is a contractile tube, each end of which is prolonged into a vessel. 

 In the Appendicularice (Copelata) the heart is placed transversely, 

 and is pierced by only two slits. The so-called vascular system of 

 the Ascidians consists of a rich net-like system of lacunae, which 

 cannot, however, be said to have special walls. 



The nervous system is reduced to an elongated ganglion (cerebral 

 ganglion) placed on the dorsal side of the branchial cavity. From 

 this ganglion nerves are given off, especially forwards towards the 

 entrance of the pharyngeal sac; but unpaired sense nerves and 

 lateral and posterior nerves also arise from it. In the Copelata and 

 Ascidian larvae the cerebral ganglion is more complicated. In these 

 animals it has the form of a cord, primitively containing a cavity, 

 and divided later by constrictions into three regions, and is connected 

 with ganglia in the tail (fig. 563). The anterior conical part of the 

 t>rain gives off paired sensory nerves to the region of entrance into the 

 branchial sac ; on the median globular part are placed the auditory 

 vesicle and a stalked ciliated organ ; while the attenuated posterior 

 part gives off two lateral nerves to the atrial canals, and is prolonged 



* Th. Chandelon, "Kecherches sur nne annexe du tube digestive des Tuniciers." 

 JBull. de Vacad. roy. de Bclgique, Tom. XXXIX., 1875. 



f Cf. Besides Kowalevski I.e. Kupffer. " Zur Entwickelung der einfachcn 

 Ascidien." Arch, fur mikr. Anat., Tom. VIII. 1872. 



Lacaze-Duthiers, Arch, de Zool. experim., 1874. 



