42 



PROF. AGASSIZ'S 



[Pi. ATM XXXV BtrnrxNO 01-- CAMPANULA.!^.] 



after having continued free fora certain time, they 

 become attached, and then the whole mass is de- 

 pressed and enlarged into a disc-like body, the 

 centre of which is somewhat prominent; rises 

 then more and more, and begins to be transformed 

 into a little stem ; and this little stem will open 

 . above, and form a termination, like that of the 

 commoa buds of Campanulariae (Plate XXVIII.) 

 that is to say, an animal with an internal cavity 

 We have thus again a beginning of one of those 

 complicated stems, which, by the multiplication of 

 their buds, form communities of animals, of two 

 kinds, viz: such as are individuals similar to 

 the animal at the end of the main stem, and 

 others from which a free generation is produced, 

 and which, after remaining free for a certain time, 

 go on to repeat the same process of branching and 

 budding. 



In the Tubulariae (Plate XXX, fig. A) we have a 

 similar growth. One of these bunches of eggs, 

 when examined in its immature condition in its 

 earliest formation, (Plate XXX, fig. F) is simply 

 a branch with lateral buds, and the digestive cav- 

 ity communicates freely with all these little buds. 

 But their interior mass assumes gradually a more 

 rounded form, and is successively enclosed in the 

 external mass, which will enlarge, and then there 

 will be finally isolated eggs developed, in the form 

 of bunches, when upon the summit of every one 

 of them a distinct animal envelop is formed, 

 which extends downwards upon the yolk as the 



internal mass can be considered as a yolk and 

 after it has grown so as to appear like a cup, with 

 tentacle-like appendages, the little animal is freed, 

 and has a structure like the young Medusa, as it 

 is figured from a Campanularia, in Plate XXXV, 

 figures T, P and Q. The whole process of budding 

 in this animal is shown in figures A, B, C, &c., 

 (Plate XXXV) first, the changes which regular 

 common buds undergo in their development, and 

 next, (Fig. E to G), the changes of the eggs prop- 

 er, with their animal envelop surrounding the 

 yolk, and finally dividing into tentacle-like appen- 

 dages below. The internal cavity being formed 

 by the changes which the remnant of the yolk 

 undergoes. The young animals which are derived 

 in this way in Tubularia; and Campanulariae, from 

 egg bunches, are so similar to the free buds from 

 Corynae, Podocorynae and Syncorynae,( Plate XX, 

 figures A, B and C), that their analogy cannot be 

 mistaken. This resemblance can even be recog- 

 nized in stages of growth not further advanced 

 than these, (Plate XXXV, figs. T, P, Q). Some 

 Medusas occurring on these shores for instance 

 the genus Stomabrachium have a very close re- 

 semblance to those germs of the Campanulariae 

 (Plate XXVIII), and Medusae, with only four arms 

 and four tubes diverging from the central cavity, 

 with fringes all round : and I should not be sur- 

 prised at all, if Stomabrachium was finally found 

 to be the free Medusae-like generation of Campa- 

 nularia;. But now as the affinity between all these 

 Polypi (Plate XX, XXVIII and XXXV) and the 

 Tubulariae (Plate XXX) is very clearly shown, 

 and as on that account these animals are all con- 

 sidered as belonging to the class of Polypi, though 

 they give rise to animals so closely allied to Medu- 

 sae, the question arises how far Tubulariae itself 

 can be considered as strictly belonging to the class 

 of Polypi, or whether it would not be more nat- 

 ural to view it as a type of Medusae, furnished 

 with a permanent stem. 



The only objection to this is, that true Medusae 

 are not formed in the same way as Medusae like 

 free buds of Coryne, Podocoryne and Syncoryne 

 (Plate XX.) These have arisen from buds grow- 

 ing upon Polypi-like stems, though they are final- 

 ly Medusae-like animals; whilst true Medusae are 

 multiplied by transverse division of Polypi-like 

 stems, which can have no influence upon our ap- 

 preciation of their real structure; so that the ques- 

 tion properly is, whether there can be real Medusae 

 with a stem, or not. We have, therefore, in this 

 stage of the investigation, before deciding one way 

 or anotherj to compare the true Medusae (Plate 

 XXXVII and Plate XXVIII, fig. C) with those 

 Polypi, the Tubularia, (Plate XXX), when it will 

 be seen that their structure agrees in every respect 

 but that one, that the Tubularia, with its crown, 

 rests upon a stem, whilst Medusae proper are en- 

 tirely free. The great difference there seems to be 

 in the forms of these animals is more apparent 

 than real, the cavity which hangs below the ten- 



