74 REMARKS UPON APPENDICULARIA AND DOUOLUM 



the respiratory, the anus opening on the dorsum ; and secondly, that 

 there is a long caudal appendage. 



As to the first difference, it may be observed, that, in the genus 

 Pelonaia, an undoubted Ascidian, there are indeed two apertures, but 

 there is no separation into respiratory and cloacal chambers. Suppose 

 that in Pelonaia the cloacal aperture ceased to exist, and that the 

 rectum, instead of bending down to the ventral side of the animal, 

 continued in its first direction and opened externally, we should have 

 such an arrangement as exists in Appendicularia. 



With regard to the second difference, I would remark, that it is just 

 the existence of this caudal appendage which makes this form so 

 exceedingly interesting. 



It has been long known that all the Ascidians commence their 

 existence as larvje, swimming freely by the aid of a long caudate- 

 appendage ; and as in all great natural groups some forms are found 

 which typify, in their adult condition, the larval state of the higher 

 forms of the group, so does Appendicularia typify, in its adult form, 

 the larval state of the Ascidians. 



Appendicularia, then, may be considered to be the lowest form of 

 the Tttnicata ; connected, on the one hand, with the Salpce, and on 

 the other with Pelonaia, it forms another member of the hypothetical 

 group so remarkably and prophetically indicated by Mr. MacLeay, 

 and serves to complete the circle of the Tunicata. 



88. Doliolum. — This name was given by Otto ^ to a free-swimming 

 gelatinous case, altogether structureless, of which a single example 

 was found by him in the Gulf of Naples. Its nature is altogether 

 unknown, for it is hardly justifiable, in the face of Otto's words, " Die 

 Rander sind aber vollig glatt ohne alle Spur von Zerreissung, nirgend 

 sieht man inwendig Rauhigkeiten wo die Eingeweide angessessen haben 

 konnten und die aussere Haut geht ohne Unterbrechung in die innere 

 iiber," to assume with MM. Quoy and Gaimard, that it is only a Biphore 

 whose intestines have been destroyed by a parasitic Phronima. 



Furthermore Otto states that the animal moved by a " worm-like 

 contraction of its walls," which by no means describes the mode of 

 contraction of the Salpce, with which animals he was perfectly ac- 

 quainted, and with a mutilated specimen of which, he expressly states 

 he might, except for its peculiar motion, have confounded the form he 

 describes. 2 



' Nova Acta Acad. Curiosorum t. xi. pars secunda, pp. 313 and 314. 



- Prof. E. Forbes informs me that a body answering precisely to Otto's description, was 

 found by him, occurring in considerable numbers, on the coast of Scotland, and was even- 

 tually discovered to be nothing more than the detached siphonic tubes of Soknocurtis 

 strinllatus. 



