HISTORY OF RESEARCH. lxxiii 



which possessed considerable flexibility, consists of two layers: (1) an inner layer 

 of considerable thickness, generally marked by transverse lines which meet on the 

 upper and lower surfaces of the cells so as to form a zig-zag line, but in a few cases 

 quite smooth (as in M. Sedgwickii, M. convolutus, etc.) ; and (2) an upper layer 

 consisting of two thin lamellas, so thin that the ornamentation of the inner layer 

 is seen through. This outer layer is rarely preserved. The same two layers 

 occur in Betiolites, but the double character of the upper layer is not yet 

 determined. 



In this paper also Richter was the first definitely to describe and figure as an 

 independent structure in the genus Monograptus the initial Graptolite body now 

 known as the " sicula." He calls it the foot or haft-organ. The shape of this " foot " 

 — pointed, cone-like, rounded at the lower end — is admirably given in his figure 

 of M. priodon, and he recognises the fact that the canal arises from this " foot." 

 Richter also observes that the presence of the " foot " at the base of single- 

 branched forms shows clearly that they are independent forms, and not merely 

 branches of forms belonging to compound genera. 



Richter considers that the axis of Graptolites is solid and of a fibrous 

 structure, lies in a groove of the inner skeletal layer, is covered by the outer 

 double one, and consists of as many parts as there are rows of cells. Even 

 when the groove is sinuous, as in D. teretiusculus, the axis is quite straight. In 

 Diplograptus he holds that there is only one canal and one axis, and he does 

 not agree with Hall that in Pkyllograptus there are four of each. The peculiar 

 structure of the cells in D. teretiusculus, as interpreted by him, is described in 

 detail, and illustrated by figures. Examples of the varieties of apertural ornamen- 

 tations are given, especially in the case of Bastrites. These, he considers, are 

 formed of the double upper layer. He believes that in Bastrites the apertures of 

 the cells, which scarcely project beyond the common canal, are situated in the axil 

 of the spine, the " cells " of previous authors being merely ornamental processes. 



As regards the development of the Graptolites, he observes that nothing 

 like the reproductive capsules described by Nicholson and Hall has been found 

 in Germany; but he notices the occurrence of isolated "feet" with long, 

 lash-like threads at their pointed ends. In Monograptus the first cell arises on the 

 ventral side of the "foot"; in Diplograptus a cell arises from each side of the 

 broader end of the " foot," but at different levels. He has noticed, in association 

 with Graptolites, great numbers of spherical bodies, apparently surrounded by a 

 double membrane, but he does not offer any suggeston as to the nature of these 

 bodies, or the cause of this association. 



His views of the mode of life of the Graptolites are remarkable. He thinks 

 that the "foot" was movable, and could be turned upwards or downwards. When 

 turned downwards it could be used to support the polypary vertically, by sticking 

 into the mud. Some species, perhaps, could move freely from place to place, which 



