268 PKOGKESS OF MICBOSCOPICAL SCIENCE. 



differentiation of its csenosarc, or common living bond by which the 

 individuals of the colony are organically connected. And just such a 

 colony would, under this view, a graptolite be, waiting only for the 

 development of hydrotheca to raise it into the condition of a plumu- 

 larian. Bringing now the evolution hypothesis to bear upon the 

 question, it would follow that the graptolite may be viewed as an 

 ancestral form of the Sertularian hydroids, a form having the most 

 intimate relations with the Rhizopoda ; that hydranths and hydrothecae 

 became developed in its descendants ; and that the rhizopodal grapto- 

 lite became thus converted in the lapse of ages into the hydroidal 

 Sertularian. This hypothesis would be strengthened if we found it 

 agreeing with the phenomena of individual development. Now such 

 Plumularida as have been followed in their development from the egg 

 to the adult state do actually present well-developed nematophores 

 before they show a trace of hydrothecse, thus passing in the course of 

 their embryological development through the condition of a graptolite, 

 and recapitulating within a few days stages which it took incalculable 

 ages to bring about in the palfeontological development of the tribe. 

 I have thus dwelt at some length on the doctrine of evolution, because 

 it has given a new direction to biological study, and must powerfully 

 influence all future researches. Evolution is the highest expression 

 of the fundamental principles established by Mr. Darwin, and depends 

 on the two admitted faculties of living beings — heredity, or the trans- 

 mission of characters from the parent to the offspring ; and adaptivity, 

 or the capacity of having these characters more or less modified in the 

 offspring by external agencies, or it may be by spontaneous tendency 

 to variation. 



Coal under the Microscope. — Those who are interested in micro- 

 scopical palaeontology will remember with what pleasure they read 

 Professor Huxley's lecture published on this subject some years since. 

 Since that time, of coui'se, many changes in palaeontology have taken 

 place, and in none more than ifi our views of the coal structures. 

 Hence Professor Williamson, F.R.S., was quite justified in again 

 going over the ground of Professor Huxley, as he did at the Bradford 

 meeting of the British Association. In his evening lecture Professor 

 Williamson said that Professor Huxley, in referring to the numerous 

 small bodies met in some coal mines, spoke of these bodies under the 

 name of sporangia, or spore cases. Now he (Professor Williamson) 

 had come to the conclusion that they were all spores of two classes — 

 the larger ones called macro-spores, and the smaller ones micro-spores. 

 A large number of the plants, if not all, found in the coal-measures 

 belonged to the cryptogamic plants, in which was foimd no trace of 

 seeds or flowers. The reproductive bodies that took the place of 

 seeds were little bud-like structures, to which the name of spores was 

 given. In a certain class of those plants, the club-mosses for instance, 

 were two kinds of these spores. The sporangia of club-mosses and 

 similar plants never became detached from their parent stem. They 

 burst and liberated multitudes of contained spores, which were objects 

 like those so abundant in many coals. But these spores did not play 

 so important a part in the formation of coal as Professor Huxley sup- 



