Messrs. Young on new Carboniferous Polyzoa, 333 



to careful investigations, the class of the Bryozoa* is now 

 also referred). 



Further, the type of development of the central nervous 

 system, the axial cord or [the chorda doraaUs present in many 

 species, the relation of the alimentary tube to the branchial 

 sac [Amphioxus)j are all exceedingly exact, repeatedly con- 

 firmed, and extremely important facts, indicating tliat the class 

 Tunicata presents the fundamental form from which has been 

 developed the type of the Verteljratat, hitherto standing iso- 

 lated in the systems of the animal kingdom. 



The entire absence of remains of Tunicata in all geological 

 formations will probably for ever prevent our knowing the 

 transition-forms which united the different kinds of Tunicata 

 with the lowest Vertcbrata {Amj)hioxus) . 



Considering all that has been said, I give Oscar Schmidt's X 

 view, according to which the Tunicata form a special class of 

 Protovertebratay the preference over all other opinions. 



XLII. — On new Carhoniferous Polyzoa. By Professor John 

 Young, M.D., and Mr. John Young, Hmitcrian Museum, 

 University of Glasgow. 



[Plates IX. & IX. bis.'] 



In the number of the 'Annals and Magazine of Natural 

 Histoiy' for May 1874 we described the structure of the Poly- 

 zoon which was named MUlejjora gracilis by Phillips, Cerio- 

 j>ora gracilis (Phillips's species), Moms's Catalogue, Vincu- 

 laria gracilis by others ; and we showed that the stmcture 

 was such as to justify the institution of a new genus. We 

 have now examined Ceriopora rhombifera^ Phillips, and have 

 detected a central axis in it also, this structm-e being absent 

 in C. similis and C. interporosoj Phillips. In the two latter 

 species the cells tenninate in a mass of cancellated calcareous 

 tissue of varying amount, but never forming a columnar, far 

 less a tubular axis. We prefer therefore to leave them in 

 the genus Ceriopora^ transferring C. rhombifera to our new 

 genus Rkabdomeson. After the publication of oui* former 



• Chiefly on the basis of the remarkable investigations of Nitsche on 

 Aleyonellafungosa, Pall. See also ^leni. Acad. St. P(5tersb. vol. xv. p. oO. 



t With respect to this, see Hackel, Gen. Morphol. Bd. ii. p. cxvi et 

 seq., and p. 413 et seq. 



X Vergl. Anat. 6te Aufl. 1872, p. 248. See also ilackel, Naturl 

 Schopfungsgesch. 4te Aufl. pp. 46G, 407, Taf. 12, 13. 



