HISTORY OF RESEARCH. xvii 



allied to the Ce})lialoj)ods. He cites the following arguineiits in .su[)port of his 

 opinion : 



(!) In some species there is a single roAV of cells, in others a double series. 



(2) No Graptolite has a large terminal chani1)er like that of the Cephalopoda. 



(3) Each Gra})tolite cell has its independent opening. 



(4) Certain species of Graptolites were attached to the sea floor, as appears 

 to be evident from Hall's figures. 



Barrande agrees with Nilsson that the Graptolites must be regarded as 

 belonging to the class of the rol3'paria, but that not enough is known to determine 

 exactly to what family they belong. He is inclined, however, to agree with 

 Dr. Beck that they should be grouped Avith the Pennatulinge, near the genus 

 Virgiilaria. 



2. General Form. — As regards the general shajK^ of the Graptolites, Barrande 

 recognises only two structural forms, viz. (1) the single-celled species, (2) the double- 

 celled species ; the former being straight or curved either spirally or conically, and 

 the latter being always straight. 



3. Solid A,r!s or Vircjula. — Barrande, although not the first to observe the 

 important body known as the solid axis, was the first to discern its invariable 

 presence in Gra])tolites, to describe its constitution, and to give it its name. He 

 Avrites, " Graptolites are always provided with a solid axis. This axis is cylindrical 

 and fibrous, and may be prolonged beyond the cellular part in certain mono- 

 prionidian forms {Gr. colonus). In the double-celled forms also the axis is 

 similarly prolonged, and is probably double, the tAvo portions possibly forming a 

 much flattened tube between the tAVO series of cells {Gr. palineus).'' He considers 

 it possible, judging from the upper part of the axis in Gr. pal incus, that each of these 

 portions may consist in its turn of tAvo layers, Avliich have become separated by 

 decomposition. In (JladioUtcs, hoAvever, Barrande notes that he could discern 

 no true solid axis. 



4. Coiiimoii Canal. — Barrande first applied the name of " common canal " to 

 that tube-like portion of a Graptolite Avhich lies betAveen the axis and the individual 

 cells. In the doul^le Graptolites there appear to be tAvo common canals, (juite 

 independent of one another, and Barrande gives drawings of cross-sections of 

 Gr. priodon and Gr. jMlmeus to illustrate the simple and double nature of this body. 

 In Gladiolites there is only one median canal. As regards the function of this 

 canal, Barrande is (fuite definite. He asserts that " this space enclosed the body 

 of the poly}), and from it arose the individual germs living in the cells." " It 

 served as a conveyance of connnon nutrition, and also as transport for the new 

 germs." 



T). Gi'llnh's. — The individual cells, or cellules, are in intimate ctmnection 

 Avith the connnon canal, but each germ is individualised, and constructs a cell Avilh 

 solid Avails for itself. These cellules are inclined to the axis at various angles, are 



c 



