Mr. Robert Garner's Malucological Notes. 36.3 



tentacles just mentioned are analogous to those surrounding 

 the orifices of the respiratory tubes in bivalves ; and that enig- 

 matical part, the endostyle, may represent the crystalline style 

 applied to its use (mechanical support), or at least so much of 

 it as is retained after the loss of the larval appendage. The 

 larval Ascidian, or the Appendicularia, constitutes a very in- 

 different vertebrate — the tail in the latter bent forwards at an 

 acute angle to the body or towards the mouth, and its nervous 

 cords (if such they be) seeming scarcely continuous with the 

 cephalic ganglion, and having alternate instead of opposite 

 ganglia, more unlike the vertebrate or articulate type in this 

 respect than are the nerves in the arms of the Sepia or Argo- 

 naut *. 



Bivalves would differ little from the Ascidian, provided the 

 test and mantle of the latter were slit ; but in the former the 

 "branchiai are more differentiated and the circulatory organ 

 more perfect, shelly valves and muscles to close them are 

 superadded — also a foot in most species, developed according 

 to the amount and kind of locomotion required. There is 

 in bivalves no true head ; but the mouth is furnished with lips 

 and two laminated and ciliated palps on each side, distinct 

 from the branchias but of similar structure, the lips proper 

 sometimes specialized (as in Pecten). 



Amongst bivalves the above remarks only partially apply 

 to the Brachiopoda, which, if we endeavour to trace their 

 genetic affinities, present us with some difficulties. They 

 have been considered to have the same relationship to, or 

 descent from, the Bryozoa as the Lamellibranchiate bivalves ; 

 but if so, it must be in a different line, and without the inter- 

 vention of the Ascidise. It may be questioned what relation 

 the upper and lower valves of Brachiopods bear to the right 

 and left valves of the ordinary Lamellibranchiates. The cross- 

 ing of the principal adductor muscles in the Lingula, and their 

 median union in some Terehratulce^ the compression of the 

 body and arms or tentacles in Brachiopoda generally, in the 

 opposite direction to the arrangement of the body and corre- 

 sponding parts in the Lamellibranchiata, the perfect lateral 

 symmetry in the former, and a tendency to division, seen in 

 foramina J notches, or seiJta, in several species (as in T. dij^Jiga), 

 whilst there is often a difference, in some respect or other, 



* "Onthe Genus Appendiadnria,'^ by E.L. ]Mo9s,Linu. Trans. vol. xxvii. 

 part 2. See also Ussow's Zool.-Embrvol. Investigations (by Dallas), 

 Ann. ife Mag. Nat. Hist., Feb. and May 1875. The last writer is decidedly 

 against the molluscous nature of the Ascidia ; and so are others ; but the 

 validity of this opinion depends upon the accuracy of minute and difficult 

 researches upon the nervous ganglion and other parts, and the opposite 

 conclusions of Mr. Hancock are perhaps as i-eliable. 



