POLY1PIFERA. 



45 



will, presently, be more particularly de- 

 scribed. From this disposition it results that 

 the contents of the stomach can pass as far 

 as the extremities of these four vessels, and 

 by means of the transverse canal can be trans- 



Fig. 50. 



2. The same viewed obliquely, showing the situa- 

 tion of the mouth e ; h, the transverse canal which 

 brings the four vessels into communication. 



3. The same seen from below. 



4. The four bands or vessels contracted a little, 

 giving to the embryo a subquadrate outline ; viewed 

 from below. The embryo is now no longer spheri- 

 cal, but flattened, as well as subquadrate. 



5. The embryo viewed obliquely from above ; the 

 superior and inferior parietes drawn together ; the 

 stomach projecting through the mouth. It now 

 presents the form of a Greek cross, owing to the 

 great contraction of the longitudinal bands or ves- 

 sels. 



6. The embryo placed inverted with respect to Fig. 

 1 ; the stomachal cul-de-sac, which becomes the 

 body of the polype, completely protruded. 



7. An ideal transitory figure. 



8. The embryo become fixed. The internal row 

 of tentacles beginning to protrude. 



9. The same more advanced. The two rows of 

 tentacles further developed. 



A series illustrating the development of Tubularia by 

 free gemmce, after the detachment of the embryo 

 from its peduncle, in continuation of that in the 

 preceding cut. The same letters indicate similar 

 parts in all the figures in this and the preceding 



Fig. 1. An embryo detached and moving in the 

 water like a Medusa, seen in profile ; in addition to 

 the four vessels, whose development is demonstrated 

 in the foregoing series, eight other canals (jf) are 

 now perceptible ; these belong to the external enve- 

 lope. 



ferred from one to the other. Professor Van 

 Beneden observed a fluid containing globules 

 moving in this direction in their interior. The 

 communication between the longitudinal ves- 

 sels and the stomachal cavity, and their inter- 

 communication by means of transverse canals, 

 is another arrangement exactly similar to what 

 exists in the adult Medusae. 



The outer membrane presents eight longi- 

 tudinal canals, which are found to be filled 

 with cellules, but in which no movement has 

 been observed. It is to the presence of these 

 longitudinal bands that the embryo in this 

 stage of its development owes its resemblance 

 to certain fruits, more particularly to a 

 melon. 



From the anterior part proceed four ap- 

 pendages (d), which were still undeveloped 

 at the period of the detachment of the young 

 polype, but which insensibly unfold them- 

 selves. These are the tentacula. In the centre 

 there projects a rounded opaque body (b), 

 generally of a red or yellowish tinge, which 

 is the stomach. This viscus communicates, 

 as has been stated above, with the four lon- 

 gitudinal vessels, and is the only opaque part 

 of the embryo. It opens in front by an orifice 

 which constitutes the mouth ; the whole 

 organ is eminently contractile, turning itself 

 in all directions like the body of a Hydra, 

 sometimes elongating itself like a worm, ami 

 at others shrinking so as to be almost imper- 

 ceptible. 



If the embryos examined in this condition 

 be vigorous, their movements are very varied, 

 and the forms that they assume extremely 

 singular. The regular contractions above 

 noticed are the most simple actions ; the two 

 poles separate and approach each other alter- 

 nately, whence results the progression of the 

 little creature. But this contraction may be 

 carried to a still higher degree : the rounded 

 stomach in the middle of the embryo not only 

 contracts itself in every direction, but it seems 

 to turn itself in the middle of its transparent 

 envelope like a worm in search of a passage 

 by which to get out ; and at length it pushes 

 its free extremity through the opening in front 

 of it, and elongates its body still more until 



