DEVELOPMENT OF TUBULARIA CORONATA. 89 



now be seen four other tubercles (fig. 43, c, c), which become developed 

 like the preceding; but instead of compressing the vesicle, a, they 

 surround it, and ultimately completely enclose it. They are united 

 together by a thin membrane, so as to present the appearance of a trans- 

 parent vase, having four longitudinal prominent bands, the free edge 

 slightly enlarged and rounded, a pedicle in the middle like the stem of 

 the vase, and the transparent vesicle lining its interior throughout 

 (fig. 43, E). 



(203.) The different phases of the mode of development above de- 

 scribed, however, will be best understood by a reference to the series of 

 figures which we have appended, carefully copied from Professor Yan 

 Beneden's elaborate illustrations. 



(204.) The young Tubularia has now assumed the appearance of a 

 Beroe, and in this condition has doubtless been often mistaken for an 

 individual belonging to the class Acalephae, to be described in the next 

 chapter ; lively contractions of its body are frequently witnessed, although 

 it still remains attached to its pedicle. 



(205.) At the extremity of each of the four longitudinal vessels a 

 little tubercle is next developed (fig. 43, F, e), which, as it becomes elon- 

 gated, is converted'into a tentacle ; or sometimes, as in Eudendrium, by 

 its bifurcation, two tentacula are formed from each tubercle. 



(206.) At this period of its development the young Tubularia spon- 

 taneously detaches itself from the parent stem, presenting, at the 

 moment of its separation, the appearance of a balloon, or rather, of a 

 melon (fig. 43, G). Its contractions become more and more lively; and it 

 is by the aid of these movements that its separation is effected. The two 

 poles of its globular body may be seen to approach each other, and to 

 separate alternately with a movement of systole and diastole, similar to 

 what is observable in many Acalephse. No traces of cilia are observable 

 either externally or in the interior of its body. In this condition it 

 presents an external covering, which is, so to speak, merely a derivation 

 from the integument of the parent-polyp ; this covering presents some- 

 what more consistence than the internal parts, and is open in front. 



(207.) A second membrane lines the preceding throughout its whole 

 extent ; like the former it is quite transparent, and at the anterior open- 

 ing is prolonged internally to a little distance, forming a sort of funnel. 

 These walls enclose four vessels (fig. 43, H, c), which extend from the 

 base of the embryo, and open in front into the hollow zone from which 

 the tentacula take their origin. These longitudinal vessels, therefore, 

 communicate with each other by a transverse canal, and at their origin 

 open into the central or digestive cavity. Prom this disposition it re- 

 sults that the contents of the stomach can pass as far as the extre- 

 mities of these four vessels, and by means of the transverse canal can 

 be transferred from one to the other. Professor Van Beneden observed 

 a fluid containing globules moving in this direction in their interior. 



