ASCIDIACEA. 25 



not take place, the animal remaining throughout life attached 

 by a stalk which arises close to the mouth (Fig. 19, 2). 

 The following classification has been adopted : 



Order 1. Ascidiacea. 



Tribe 1. Ascidiae simplices, Monaseidia. 

 ,, 2. Ascidiae compositae, Synascidia. 

 ,, 3. Ascidiae salpaeformes, Ascidiae Luciae. 



Order 2. Thaliacea. 



Sub-order 1. Hemimyaria, Salpida. 

 2. Cyclomyaria, Doliolida. 



Order 3. Appendiculariae (Perennichordata, Larvacea, Cope- 



lata). 



Order 1. ASCIDIACEA (TETHYODEA). 



Fixed or free-sivimming , solitary or colonial Tunicnta, which in 

 the adult are never provided with a tail and have no trace of a 

 notochord. The free- swimming forms are colonies and the solitary 

 forms are fixed. 



The test is permanent and well developed ; as a rule it increases 

 with the age of the animal. The musculature of the mantle is 

 in the form of an irregular network, there being no regular circu- 

 lar bands. The pharynx is large and well developed. Its 

 walls are perforated by numerous apertures opening into a 

 single atrial (peribranchial) cavity, into which the anus opens 

 and which communicates with the exterior by an atrial aperture. 

 The colonial forms reproduce by gemmation, and in most the 

 sexually produced embryo develops into a tailed larva. The 

 order is divided into three groups, the Ascidiae Simplices, the 

 Ascidiae Compositae and the Ascidiae Salpaeformes. 



These three groups can only be regarded as tribes, for they are closely 

 interrelated, and are distinguished, the two first oy the presence or absence 

 of the power of budding and the last by being free-swimming. If other 

 and more general anatomical characters w r ere taken, quite a different 

 grouping of the families would be obtained, and there can be no question 

 that some of the families of synascidians are more closely related to cer- 

 tain families of the monascidians than to each other. But if in the grouping 

 of the families account were taken of these facts it is difficult to say that 

 a more natural system of classification would be obtained ; cross-relation- 

 ships between the groups constituted would still exist, and would by 

 many be considered to be of sufficient importance to justify a different 



