100 TUNICATA. 



fully developed. The young generations, therefore, now have the 

 double task of caring for their own already fertilized eggs and of 

 fertilizing those of the succeeding generations. 



Order 1. COPELAT.E* (Ascidians with larval tail). 



Small free-swimming Ascidians of long oval form, with swimming 

 tail ; they resemble in the whole of their organization the larvae of 

 other Ascidians (fig. 562). The anus opens directly to the exterior 

 on the ventral side. The pharyngeal sac is pierced by only two 

 branchial slits. The heart has two slits and no vessels. The 

 ovaries and testes lie in the hind part of the body, close to one 

 another, and are without ducts. The elongated cerebral ganglion is 

 divided by constrictions into three parts; it is connected with a 

 ciliated pit and an otolithic vesicle, and is prolonged into a nerve- 

 cord of considerable size. The latter is continued into the tail, at 

 the base of which it swells out to a ganglion ; in its further course 

 it forms several small ganglia, whence lateral nerves pass out. In 

 consequence of a torsion of the axis of the tail, the originally 

 dorsally-placed caudal nerve comes to have a lateral position. The 

 segmentation of the nerve-cord in the tail (as shown by the gang- 

 lionic swellings) corresponds to the segmental divisions of the muscles, 

 which recall the myotomes of Amphioxus. The large chorda (uro- 

 chord), which extends along the whole length of the tail, constitutes 

 another point of resemblance to Amphioxus. 



Some species have a pellucid gelatinous covering, comparable to 

 a shell. The development of these small animals, which were 

 formerly erroneously held to be larvae, has been insufficiently 

 investigated. 



Fam. Appendicularidae. Oikopleura Mertens (Appendicnlaria Cham.), Oi- 

 copliocerca G-egbr., OLfurcata G-egbr., Fritillaria Fol. The integument forms 

 a hood-like reduplicature in front ; the tail one and a-half times as long as the 

 elongated body ; the endostyle is curved. Fr. furcata C. Vogt., Fr. formica 

 Fol, Koivalevskia Fol. Without heart and endostyle. Kectum absent. K. 

 tennis Fol, Messina. 



Order 2. ASCIDI.E siMPLiCES.t 

 This order comprises solitary forms as well as branched stocks. 



* Cf. C. Gegenbaur, " Bemerkungen liber die Organisation der Appendicu- 

 larien.' r Zeitscli. fur miss. Zool., Tom. VI., 1855. 



H. Fol, " Etudes sur les Appendiculaires du detroit de Messine." Mem. Soc. 

 de Phi/s. et d'Hist. Nat. de Geneve, Tom. XXI.. 1872. 



f Cf. besides Lacaze-Duthiers I.e., C. Heller, " Untersuchungen liber die 

 Tunicaten des Adriatischen Meeres, I., II., III.," Dcnkschr. der k. Akad. 

 tJcr Wissensch. Wien, 1874-1877. 



