396 R. T. JACKSON TEACHING PALEONTOLOGY 



of morphological facts which can only be conferred by a large and thorough 

 acquaintance with anatomy and embryology. But under this aspect the 

 palfieontology of the Invcrtehrata has yet to be created." 



If the simpler and ancestral types of our living animals are to be 

 known^ it is to the fannas of the past, or the fossils, that we must look 

 for them. If fossils are to be studied with intelligence, we mnst con- 

 stantly compare them with living forms, where, with the soft parts still 

 in place, we come to have a full appreciation of the relation of soft and 

 hard parts that can not be attained from a study of the fossil alone. In 

 other words, a combined study of living and fossil forms gives the fullest 

 understanding of each and gives a rounding out of our knowledge of a 

 group of animals that it is impossible to get by a study based only on 

 either the fossil or the recent. A course of study based on such principles 

 should appeal to the purely paleontological student and also to the zoolog- 

 ical student as well; for it would be helpful to them in future work, 

 whether that were in the line of the fossil or the living organisms. Such 

 was the method of work laid down by the great master, Alpheus Hyatt, 

 and folloAved by those who got their inspiration from him. 



In an address of this nature, with many other speakers and limited 

 time, only a few points can be touched on, and briefly at that. The value 

 of stages in development exists, it is believed, through all organisms and 

 also more or less throughout the life of all organisms, but here consider- 

 ation will be given only to a few invertebrates. The adult of any given 

 type presents a certain complexity of structure differing greatly with the 

 type. How did it come to be what it is, and what are the meanings of 

 the structural details in relation to associated forms? The adult came 

 to be what it is by growth from the young, and during this growth char- 

 acters are progressively added until the full species features are attained, 

 and may even be continued up into the old age of the individual. Such 

 additions of characters, or stages in development, are of first importance 

 from the light they throw on structure, on morphological relations, and 

 on genealogical affinities. 



In Protozoa, as unicellular organisms, it has been thought that stages 

 in development do not exist. However, J. A. Cushman has shown abun- 

 dantly, in studies of recent and fossil Foraminifera, that there is a devel- 

 opment of the test in which, by the addition of chambers and ornamen- 

 tation of the same, a series of stages is presented quite as truly as may 

 be seen in the higher groups, such as mollusks. 



In the compound fossil corals, Pleurodictyum and Favosites, the late 

 C. E. Beecher showed that the young has a simple cup, and during 

 growth other cups were added progressively, with pore connections sim- 



