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PROCEEDINGS OF THE 



[July, 1857. 



been subjected to pressure to so great a degree as completely to 

 alter their form. These are transverse sections of Graptolitic 

 stems, and are trilobate, like the transverse section of a rod in an 

 Echinocidaris larva, figured by Muller, Siebente Abhandlung, 

 PL 4, fig. 8. This trilobate section showed that the stems in some 

 Graptolites, at least, were like the complex rods (gitterstaben 

 Mull.) in Echinoderm Larvae, composed of three parallel rods, 

 bound together; and Mr. McCrady thought that the delicate black 

 line, often traceable along the axis of a Graptolite of the genus 

 Diprion, was not a central stem, but merely the edge of the third 

 rod, of which no other part could be seen. See Pictet's Palion- 

 tologie, PI. cviii. fig. 19, a and b. The fact that the three lobes of 

 the section in the Graptolites were not grouped together in the 

 same manner as in the rods of Echinocidaris, might be due to 

 compression; or, if this arrangement were normal, it would not, 

 in his opinion, impair the analogy. 



With regard to Gladiolites, which was composed principally 

 of a net-work structure, it was just as explicable on this supposi- 

 tion as on any other, and did not fall without the range of variation 

 which might be conceived as possible for the type of structure 

 exhibited in the Echinoderm larvae. For net-work expansions of 

 parts of main stems, are by no means uncommon among the lat- 

 ter; as, for instance, in the upper parts of the great rods in the 

 larva of Echinocidaris aequituberculata, Muller' s Siebente Jib- 

 handlung PI. 4 fig. 2. It was quite possible that such expan- 

 sions might have played a more important part in the organiza- 

 tion of mature animals of similar type. 



Mr. McCrady, in conclusion, remarked that this suggestion, if 

 proven true, would have important results. In the first place, it 

 would explain the analogies of the hitherto scarcely explicable 

 embryology of Echinoderms; and in the second, it would add a 

 new sub-order, Graptolitidce, to the class of Echinodermata. If a 

 mistaken supposition, it ought, therefore, to be disproved as soon 

 as possible. If founded in truth, a satisfactory proof of it would 

 enlarge our views of a remarkable class in the animal kingdom. 



