12 THE AMERICAN NATURALIST. [VOL. XXXII. 
lites may be, it certainly is necessary for the understanding of 
the life history of the individuals of the colonies to compare the 
graptolites with some class of living animals, and there is 
undoubtedly no other class available but the order of Campanu- 
lariæ. It also should not be forgotten that the virgula, which 
always has been considered as constituting one of the principal 
differences between graptolites and campanularians, has been 
proved to be comparable to the hydrocaulus of the first theca 
of the Campanulariz. 
Another difference between graptolites and campanularians 
has been supposed to consist in the floating habit of the former. 
This leads us to the interesting question as to the mode of 
life of the graptolites, which lately has been discussed by an 
author (Lapworth, '97) whose lifelong study of these fossils, 
both in the laboratory and in the field, gives his views the 
greatest moment. 
The peculiar mode of occurrence of the graptolites, vzz., in 
numberless multitudes of broken rhabdosomes in highly bitumi- 
nous shales, which are otherwise poor in fossils, their astonish- 
ingly wide horizontal distribution and limited vertical range, 
has often been an object of speculation. But it is now to be 
hoped that, by the light shed lately on the structure and 
development of the colonies, by the exhaustive study of their 
distribution, and especially also by the researches which recently 
have been carried on so extensively in regard to the conditions 
and distribution of life in the ocean, the clue to the understand- 
ing of their mode of occurrence will be found. The works of 
Walther (93) and Ortmann (96) have done much to make the 
results of these bionomic researches known among geologists, 
and Walther’s investigation has given the direct instigation to 
Lapworth’s valuable discussion. 
The common consensus of two generations of geologists, 
says Gurley, has been that the true graptolites (Graptoloidea, 
Retioloidea) were “ floating.” Jækel and Wiman, on the other 
hand, concluded from the heavy chitinous covering of the thecz 
and the presence of the virgula as a supporting rod that the 
rhabdosomes were not suspended, but that the colonies were 
lightly moored to the ground. Ruedemann (97) was forced to 
