APPENDICULARIA FLABELLUM. 513 



A rounJed octocyst containing a spherical otolith is at- 

 tached to the ganghoii, and a small ciliated sac, which opens 

 into the pharynx, is in close relation with it (Fig. 147, r, q). 

 M. Fol describes a number of fine tactile seta? situated around 

 the oral ajjertui-e. 



The urochord, which constitutes the axial skeleton of the 

 appendage, is transparent, rounded at each end, and bounded 

 by a delicate membrane. The remains of the cells of which 

 it is composed are to be seen in it, here and there, as ramified 

 corpuscles lodged in its periphery. 



The only muscles hitherto observed in Append Icularia 

 are two sheets of striped fibres interposed between the uro- 

 chord and the cellular ectoderm of the appendage. 



The reproductive organs occupy the rounded projection 

 formed by the posterior part of the body behind the digestive 

 canal. The testis (Fig. 147, /v) is a large cellular mass which 

 fills the greater part of the cavity of this projection in the 

 adult. When fully formed, it is resolved into spermatozoa 

 with rod-like heads about yoVo ^^ ^^^ \\\^\\. long and very fine 

 filiform tails. They escape by the dehiscence of the testis. 



I have never met with AppendlcidarirB containing ova, 

 nor do any other observers, except M. Fol, appear to have 

 been more fortunate. The latter, however, states that these 

 animals are hermaphrodite {Oikopleura dioica apparently is 

 dioecious), and that the ovary is developed later than the 

 testis.^ 



Two singular rounded patches of a cellular structure (Fig. 

 147, 11. in) are interposed between the ectoderm and the en- 

 doderm on each side of the anterior end of the endostyle. 

 Similar bodies occur in other Ascidians, but their function is 

 unknown. 



One of the strangest peculiarities of the Append I cidarim 

 is the power which they possess of excreting from the surface 

 of the ectoderm, with extreme rapidity, a mucilaginous cu- 

 ticular investment, in the interior of which, as in a spacious 

 case, the whole body is lodged. This is what was originally 

 described by Mertens as the *' house " of the Appendicularia, 



^ T must confess tliat M. Fol's fig-ures and descriptions of the ovars' and ova 

 are not satisfactory to me, and his dismissal of the subject of their development 

 in the followincj parawraph is tantaliziner : 



"Le developpement, que j'ai pu suivre jusqu'a la formation de la larve, ne 

 me parut differer en rien de celui des Ascidies ; et comme d'autre part la peti- 

 tesse de ces oeufs et la difficiUt*^ qu'on a de les obtenir les rendent peu favo- 

 rables a I'^tude, je n'ai pas juge a propos d'aj)profondir davantage ce sujet." 

 {I. c, p. 1.) 



