44 



PROF. AGASSIZ S 



they arise externally from the lower or central ca 

 rities of the alimentary canal, and are surrounded 

 by the disc, which contains the main cavity of the 

 body, and from the periphery of which the tenta- 

 cles hang down, so that here the ovaries are out 

 side of the stomach, and outside of the main cav- 

 ity, as in Tubularie, and not within the common 

 cavity, as in Polypi. 



Now in order to insist more strongly upon the 

 fundamental differences which exist between Polypi 

 and Medusae, even if we include Tubulariae among 

 the latter, let me once more call your attention to 

 the Tubularia (Plate XXX, fig. A). We have here 

 a mouth, with the anterior alimentary cavity, 

 which will assume all possible shapes, as we see in 

 these various diagrams, hanging outside of the 

 common cavity, and not within it, as in Polypi. 

 We see those bunches of eggs, arising below the 

 tentacles, between the tentacles and the anterior 

 alimentary cavity, also outside of the alimentary 

 cavity, the central cavity extending above, so that 

 the analogy is perfect in every respect. 



And as we have in the Corynas, Syncorynas and 

 Podocorynas buds, which, though growing from 

 Polype-like animals, will produce real Medusae, 

 their close resemblance to Tubularite will only be 

 an additional evidence that these must be referred 

 to the class of Jelly-fishes, and that the club- 

 shaped Polypi, in their perfect condition, are also 

 Medusae, and that their earlier stages of growth 

 are only nurses to produce real Medusas by alter- 

 nate generation. The Tubularias themselves will 

 have, however, to be considered as the lowest 

 type of Medusae, preserving something of the Po- 

 lype structure, as they are for life provided with a 

 stem, from which the crown hangs down. And 

 from this stem would arise buds similar to the ter- 

 minal animal (Plate XXX, fig. G) which would 

 remain connected with the. stem, thus forming 

 branched compound Medusas. And if this ground 

 be correct, not only Tubularia, but also Campanu- 

 laria and Sertularia shall be united with Corynas, 

 Syncorynas and Podocorynae in the class of Medu- 

 sas. Thus circumscribed, the class of Medusas 

 would present the most remarkable parallelism 

 with the class of Echinoderms and that of Polypi, 

 in both of which there are free types and such 

 as rest upon attached stems, a parallelism 

 upon which Oker has already insisted, in a general 

 way, is his classification of the animal kingdom. 



To investigate further this subject, there is a rich 

 field in this vicinity, where animals, Tubularia, 

 Companularia and Sertularia, occur all around the 

 shores of Massachusetts. 



Again, if my conjecture of the necessity of com- 

 bining these Tubularia with Medusa is correct, I 

 venture to foretell, that among those small species 

 of this class, which are found on this shore, we 

 have the Medusa-like form of the Coryna, in the 

 little Oceania of Dr. Gould's Report, whose struc- 

 ture is Mustrated in Plate XXVIII, fig. C., as I have 



ascertained by dredging, that Coryna occurs in 

 Boston and harbor. 



That Coryna has been found so seldom is be- 

 cause it lives in deep water, and is not discovered 

 unless by dredging. 



I should not be surprised at all to find also 

 Stomabrachium, as the Medusa-form of Campan^ 

 ularia, which occur all over the shores of this con- 

 tinent, and that Bongainvillia could be the Medusa 

 of Tubularia, if they produce at all a free genera- 

 tion, seems to be probable, when we consider the 

 form of its crown. (Plate XXX., fig. A.) 



As for the gradation of types in the class of Me- 

 dusa, we should consider the Tubularias as the 

 lowest, for the reasons already stated. Next we 

 should place the free compound Medusae, the Phy- 

 sophoras of Eschscholtz, which correspond to the 

 next stage of growth of Medusa, known under the 

 name of Strobila. 



[PLATE XXVI MEDUSA [ 



Next we should place the free Medusae or Disco- 

 phora of Eschscholtz, and highest the Ctenophoras, 

 as by their comb-like rows of fringes, which may 

 be considered as a lower form of Ambulacra, they 



