in the Environs of Brussels. 385 



form, 6-8 millims. in its longest diameter (fig. 4, ddd). 

 After this, viz. 7 centims. further on, two other cylinders of a 

 similar kind branch off in different directions (fig. 4, d) , in 

 all six ; but as, in each instance, one passes out behind, it 

 cannot be represented in the drawing ; while the main cylin- 

 der in its course also presents several nodular excrescences 

 which look like the gemmiparous commencements of more 

 branches (fig. 4, e). This specimen has very much the ap- 

 pearance of both the circular and compressed cylindrical forms 

 conjoined — that is, the former embracing the latter ; but 

 the tohole was encased within one and the same tuberculous 

 layer, sending off processes to cover the branches respec- 

 tively. 



Here it should be observed that although the branching has 

 not been observed in any Annelid of the present day, still 

 the process of gemmiparous reproduction is not altogether 

 absent in the Annelidans (ex. gr. Nais cirrhatula), in 

 which, it is true, the anterior segments here and there pass 

 into heads successively, while those in the intervals become the 

 bodies of the new animals. Is it possible that a lateral instead 

 of longitudinal multiplication could have taken place in the 

 older Annelidans, although hitherto not found in recent ones ? 



Again, although our knowledge of what is going on at the 

 present day is the best interpreter of what has taken place 

 during past ages, still the amount of this interpretation must 

 be in proportion to the amount of that knowledge ; and 

 although many forms have existed in past ages which do not 

 exist at the present day, and vice versa, there are modifica- 

 tions on both sides which can easily be admitted without 

 doing violence to the principle first enunciated. May it not 

 have been so here, viz. that a branched gemmiparous Annelid 

 may have previously existed ? 



Tuberculous layer. — While, however, there is a great differ- 

 ence in the form of the " central cylinder" and its varieties, 

 viz. circular, oval, and branched, all are without exception 

 surrounded by the same kind of tuberculous layer (fig. 1, aaa^ 

 fig. 2, bbb, &c., also figs. 6, 7, and 8, b) j and this, although 

 corresponding internally to the surface of the cylinder, is 

 deeply pisiform externally, where it is in contact with the 

 " concretionary crust " of sand derived from the deposit in 

 which the " tubulation " is imbedded (fig. 2, a a a, and figs. 

 7 and 8, bb). Its composition, where solid and still united or 

 in direct contact with the cylinder (figs. 6, 7, and 8), is the 

 same as that of the latter, viz. almost purely arenaceous, indi- 

 cative of its having been part of the animal itself; but in most 

 instances this material has become so friable that the whole 



