Dr. 0. Herrmann — Distribution of Graptolites. 



449 



pressed state, presents itself as a pointed, dagger-shaped organ 

 (Fig. 2 s.). In its external wall a bacilliform axis (virgula, solid axis 

 " axe solide ") is developed, and two embryonal buds soon begin to 

 sprout forth from the sicula, become converted into cells (Hydrothec^, 

 "Zahne," denticles, calycles, "cellules," "Thekorna"), and form 

 the commencements of two branches ("Arme," " Zweige," stipes, 

 branches, " Grenarne ") diverging at a definite angle. Each of these 

 branches represents a tube, the cavity of which (" Gemeinsanier 

 Canal," common canal, " Canal commun ") is occupied by the soft 

 animal proper (coenosarc). The axis lies upon the dorsal surface of 

 the branch ; opposite to it are the hydrothec^ arranged in consecu- 

 tive order (Monoprionidian Graptolites). The walls of the canal in the 

 living state were chitinous ('' Skeletbildende Substanz," " Haut," 

 " Schale," periderm, perisarc, test), and consist of three lamina. 

 In most cases the branches in growing did not continue simple, but 

 forked ; the forks thus formed might divide again, etc. By two 

 such divisions an eight-branched form is produced {DicJwgrap'tis 

 octobracMatiis, Hall, Fig. 1). It has been thought that the basal parts 

 of the branches in many ramified Graptolites were free from 

 hydrothecee, and this " naked " part has been named the stem 

 ("Stiel," funiculus, funicle). In some species these basal parts of 

 the branches are united by a chitinous membrane (Discus, central 

 disc, corneous disc, Fig. 1). 



In what follows we shall chiefly employ the nomenclature 

 established by Allman and others for the different parts of a Hydroid 

 Polyp. 



Fig. 1. Dichoffraptus octobrachiaius, JLall, tromthe Fh)/Uoffrapius-sJiales, Galgenberg, 

 Christiania. Natural size. Original. 



The Sicula. — The inconspicuous organ to which Lapworth has 

 given the name of the Sicula, and which early attracted the attention 

 of palasontologists, but under the names of " Haftorgan," "radicle," 

 etc., has received a false interpretation, has now, since the recognition 

 of its true significance, and of the part it plays in the development 

 of the polypidom, taken a prominent position among the organs of 

 the animal-colony. If we have to decide whether fragments of 

 Graptolites that may be met with belong to the single-branched 

 family Monograptidse, Lapw,, or are fragments of branched Grapto- 



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