HISTORY OF RESEARCH. liii 



there are four slender common canals, which "may or may not communicate with 

 one another." 



Calycles or ( •ellales. — The structure and form of the various kinds of cellules are 

 discussed by Hall in considerable detail, and excellent figures are given illustrating 

 the longitudinal and transverse sections of various species, especially of those of 

 Climacograptus. Hall agrees with Barrande that the cell walls are double. He 

 considers that the cellule is limited by the cell Avails, and he states that he has not 

 discovered " evidence of such cell diaphragms" as were described by M'Coy; but he 

 observes that there is " sometimes a swelling of the test of the common body below 

 the cellule, indicating an enlargement of the parts at the bases of the buds," with 

 occasionally an " undulation of the axis corresponding to this enlargement." The 

 structure of the cellules of Climacograptus is minutely discussed, and Hall concludes 

 that the cell partitions originate from the solid axis, and " appear to consist of 

 triangular plates, so that there is an apparent double communication with the 

 common body, giving not only the usual bilateral arrangement of the parts 

 generally, but a bilateral arrangement of the parts in the individual alveoles." 



The various kinds of cell-apertures are described, and the different ornaments 

 of the test — such as spines, stria?, and pustules — in the several species, but 

 few additions are made by him to the observations of Barrande on the same 

 subject. 



Mode of Reproduction. — One of the most important parts of Hall's work is the 

 section devoted to the Reproduction of the Graptolites. In it he brings to light 

 many novel facts, and by several valuable suggestions directs attention to the need for 

 further research in this direction. In 18-58 he had described certain "elongated 

 sacs with swollen extremities," which he supposed contained the ovules or germs. 

 These sacs " have scarcely any apparent substance," but are supported by numerous 

 fibres, and in one case at any rate there is "conclusive evidence that they are 

 connected with the solid axis of the parent stipe." The various figures given by 

 Hall in illustration, both in the former and in the present work, show well the 

 shape and arrangement of these "sacs." In his fig. 9 they are attached to what 

 appears to be an example of I>. Wliitfieldii. Tn other cases there is apparently no 

 ordinary cell structure on the stipes bearing the so-called reproductive sacs. These 

 forms have since been separated under the provisional title of Hallograptus by 

 Carruthers. 



Several so-called germs or " young Graptolites of extremely minute proportions " 

 are also described and figured by Hall in this work. Although they have never 

 been actually found inside any of the "sacs," he has no doubt that they were 

 derived from them. Hall's figures of these " germs" will best illustrate his views 

 on their structure. In some of his typical instances, his so-called little "sac"' 

 containing the germ of the zoophyte is practically synonymous with the body after- 

 wards distinguished by Lapworth as the sicula, though Hall considers the "radicle 



h 



