body ot the Polypiile; and the so-called perigastric fluid therein contained, wherein, the intes- 

 tinal canal of the animal is freely suspended, does not stand in any direct connexion with 

 the surrounding medium. The retraction of the Polypide into the cell is effected only, by a 

 folding (invagination) of the anterior elastic part of the endocyst, by which the so-called ten- 

 tacular sheath is produced. The case is quite different with the Rhabdopleura. Here is no 

 cinJoci/s-f at all (unless we should consider the glassy skin which closely surrounds the diges- 

 tive apparatus, to bean endocyst), consequently also no perigastric fluid; and further the cavity of 

 the cells stands in direct communication with the surrounding medium, without being closed 

 at the aperture by a skin connecting it with the animal's body. The retraction and protrusion 

 of the Polypide is therefore not effected as usual by in- and evagination, but in a totally 

 different manner, of which more hereafter. Allman has indeed (1. c.) imagined that he has 

 perceived a trace of a real endocyst of the same nature as that observed in the other Poly- 

 zoa, but he has quite certainly deceived himself. The Polypide of the Rhabdopleura lies 

 quite free in the cell, and is only attached to the colony by means of the contractile cord, 

 neither by any endocyst nor special muscles, as appears clearly enough from the fact that 

 when the contractile cord is severed, the Pol}'pide can be taken entire and uninjured out of 

 its tube with the greatest ease. 



From the anterior part of the body where the mouth is situated, yet, as will appear 

 in the sequel, not as usual in a terminal position, but rather in a ventral situation behind the 

 peculiar oval i)rominence (the bucal shield), the gullet or (rsophai/nv, (fig. 5, 14 etc. e) rather 

 short, but wide, and furnished with thick walls, proceeds right downward or backward to the 

 stomach, from which it is separated by an also outwardly apparent constriction, and by a 

 sort of internal valve (the cardiac valve). 



The Sfoniach (f.) which is simple without any armament of teeth or hard parts in 

 its interior, and furnished with tolerably thin walls, is elongated, rounded cylindrically, slightly 

 and somewhat irregularly curved, with ventral concavity, and in its anterior part, where it 

 has its greatest breadth, only a little wider than the gullet and occupying about -/a of the 

 cell's caliber (see tig. 14). In the anterior half it is of about uniform thickness, but diminishes 

 towards the posterior end (Pylorus) very rapidly, and goes imperceptibly over, after turning 

 a little to one side, into the intestine, suddenly curving itself upward and forward. The In- 

 fcstine (g) which is not by any constriction, nor yet by any interior valve (Pylorus-valve) dis- 

 tinguished from the stomach, of which it forms the innnediate continuation, is narrow, cylin- 

 drical (its thickness scarcely Vs of that of the stomach in the widest part) only slightly 

 tapering towards the end (see fig. 17) and has a tolerably straight course forward, lying close 

 to the dorsal side of the stomach and gullet, and terminates with a circular anal aperture, 

 situated just liehind the spot from which the tentacular arms proceed. Immediately behind 

 the anal aperture, between the terminal part of the intestine and the dorsal wall of the gullet, 

 which here forms a little concavity, there appeared a clear cellular body (fig. 15. r) in which 

 several evident nuclei were visible. I cannot however pronounce any decided opinion as to 



