346 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



lowest Eocene fauna secured at Upper Marlboro, Maryland, was 

 collected only after several days' active work of sieving the sand, 

 and a small pill box was sufficient to hold the entire results. 



In case these fossils can not be found in soft rock it is often still 

 possible to obtain good specimens for study. A comparatively hard 

 fossiliferous rock, when crushed in a sack with a wooden mallet, 

 will often afford fairly well-preserved fossils after the debris has 

 been washed and sieved as mentioned above. In such a case the bryo- 

 zoans, although likely to be broken into smaller fragments than 

 usual, are generally well enough preserved for accurate determina- 

 tion. If the rock is calcareous and too hard to yield to such treat- 

 ment, thin sections may be employed to determine the bryozoa. 



The separation into species of the fragmentary specimens resulting 

 from the washings can be made with an ordinary hand lens, magni- 

 fying 8 or 10 diameters. The identification of these species can also 

 be made under such a lens providing the species have already been 

 well described and illustrated. In the identification and discovery 

 of the characters of new species, however, a higher magnification is 

 necessary. 



Bryozoa in the recent seas are collected in quantity by dredging 

 (pi. 2), although a thorough search of seaweeds and shells cast upon 

 the beach or of piling and other structures exposed at low tide will 

 reveal them in considerable numbers. A prolific source of bryozoa 

 for the student is the common oyster and clam of Eastern markets. 

 Many of the specimens secured in the above ways are dead, that is, 

 they contain no living polypides. The study of such bryozoa follows 

 the various methods indicated for the fossil forms. Specimens re- 

 taining the polypide may be preserved in alcohol or formaldehyde 

 for an indefinite time before the structure of the animal itself is lost. 

 After decalcifying and embedding in paraffin, thin sections of such 

 specimens may be cut with the microtome as usual for tissues. If the 

 removal of the animal matter is desired in order to study the zooecia 

 unobscured, boiling in Javelle water as described below is necessary. 



METHODS OF STUDY. 



The relationship between the polypide or living animal and the 

 zooecium or home which it secretes for itself, is such that the study 

 of recent bryozoa embraces two distinct processes, first that dealing 

 with the anatomy of the polypide itself interpreted by the usual 

 histological methods, and second, the determination of the structures 

 belonging to the zooecia. The first is a subject upon which much re- 

 mains to be done and the attention of biologists is directed to it as a 

 favorable field for research. The second will be discussed in some de- 

 tail here because the classification of the bryozoa and the identifica- 



