366 MONTGOMERY. 
In my search for the homologies of the coelom, or pseudo- 
coel, of the Nemerteans, a search which has led me to negative 
results, I have been obliged to exceed the limits which I had at 
first intended; but it is to be hoped that this brief critical con- 
sideration of the morphological value of body cavities in general 
may throw a new light on these structures. 
Any one wishing to compare earlier views upon their nature 
may consult, outside of the text-books of Balfour, and of 
Korschelt and Heider, the following papers: 
BALFour. On the Structure and Homologies of the Germinal Layers of 
the Embryo. Quart. Journ. Micr. Sci., 20. 1880. 
BUTSCHLI. Bemerkungen zur Gastraeatheorie. Morph. Jahrb., 9. 
HAECKEL. Die Gastraeatheorie, die phylogenetische Classification des 
Thierreichs und die Homologie der Keimblatter. /exa. Zeztsch., 8. 
IpEmM. Nachtrage zur Gastraeatheorie. /dzd., 11. 
HATSCHEK. Studien iber Entwickelung des Amphioxus. Avr. zool. Inst. 
Wien, 4. 1881. 
HERTWIG, O.AND R. Die Coelomtheorie. Versuch einer Erklarung des 
mittleren Keimblattes. Jena, 1881. 
LANKESTER. On the Primitive Cell-layers of the Embryo as the Basis 
of Genealogical Classification of Animals, and on the Origin of 
Vascular and Lymph Systems. Azn. and Mag. Nat. Hist., 11. 
1873. 
IpEM. Notes on the Embryology and Classification of the Animal King- 
dom, etc. Quart. Journ. Micr. Sci..17. 1877. 
RABL. Theorie des Mesoderms. Morph. Jahrb., 15. 18809. 
WALDEYER. Die neueren Forschungen im Gebiet der Keimblattlehre. 
Berlin. klinisch. Wochenschr. 1885. 
WISTAR INSTITUTE OF ANATOMY AND BIOLOGY, 
PHILADELPHIA, Pa., July 15, 1896. 
