30 ON CLASSIFICATION. 



easily recognisable by the circumstance that their external inte- 

 gument is provided with two prominent, adjacent apertures, so 

 that they look very much like double-necked jars (Fig. 10). At 



first sight you might hardly suspect the 

 animal nature of one of these singular or- 

 ganisms, when freshly taken from the sea ; 

 but if you touch it, the stream of water which 

 it squirts out of each aperture reveals the 

 existence of a great contractile power within ; 

 and dissection proves that this power is 

 exerted by an organism of a very consider- 

 able degree of complexity. Of the two aper- 

 tures, the one which serves as a mouth is 

 often — but not always — surrounded bv a 

 circlet of tentacles (Fig. 11, c). It invariably 

 Fag. 10 —Phaihma men- i eac [g m t an exceedingly dilated pharynx, 



tula ; a, oral ; b, atrial # , 



aperture ; c, base of the sides of which are, more or less exten- 

 sively, perforated. The gullet comes off 

 from the end of the pharynx, and then dilates into the 

 stomach, from which an intestine, usually of considerable 

 length, is continued to the anal aperture. The latter is almost 

 always situated within a chamber, which opens, externally, by 

 .that second aperture upon the exterior of the test, to which I 

 referred just now. Furthermore, in all Ascidians which I have 

 examined, the first bend of the intestine takes place in such a 

 manner that, if the intestine continued to preserve the same 

 direction, it would end on the opposite side of the mouth to the 

 nervous ganglion (Fig. 11) ; in other words, the nervous gan- 

 glion would not be situated in the re-entering angle between the 

 gullet and the rectum, but on the opposite side of the gullet to 

 that angle. Therefore, the flexure of the intestine is not neural, 

 as in the Polijzoa ; but as, on the contrary, the intestine is 

 primarily bent towards the heart side of the body, its flexure may 

 be termed " haemal." And this haemal flexure of the intestine 

 in the Ascidians thus constitutes an important element in the 

 definition of the class. 



In these animals there is an atrial system, the development 

 of which is even more extraordinary than in tho Pohjzon. The 



