70 



THE AMERICAN NATURALIST 



[Vol. LV 



the terms of the more recent nomenclature used in description 

 and classification. The study of the bryozoa has developed to 

 such a degree in recent years and so many new terms have been 

 introduced which are found only in the scattered writings of 

 numerous authors, that a new compilation and exposition similar 

 to the classic work of Hincks in his ''British Marine 'Polyzoa" 

 would be useful. As far as it was compatible with the limits of 

 this treatise such a compilation and exposition have been accom- 

 plished here, and both the beginner in the study of the bryozoa 

 and the advanced worker will find great assistance in the dis- 

 criminating use of the newer anatomical terms. 



2. Of the general functions of the bryozoa, of the Cheilosto- 

 mata especially, the discussion of the hydrostatic function is 

 perhaps the most interesting because it presents the newest and 

 latest views on this puzzling subject. The extrusion and re- 

 traction of the polypide, the action of the operculum and of the 

 zocecial muscles in these activities, and the relation of these to 

 the ingress and egress of water was long a puzzle. Jullien in 

 1888 first discovered the so-called compensating sack or com- 

 pe'nsatrix under the dorsal surface of the zooecium. Since then 

 scattered studies have been made on this organ which w^as soon 

 found to be present in many species. The present authors have 

 continued this study and following Levinsen (1909) have made 

 the presence or absence of a compensatrix the basis of division 

 of the Cheilostomata into two sub-orders Anasca, without such 

 a compensating sack ; Ascophora, possessing such a sack. 



In addition to the zocccial hydrostatic system discovered by 

 Jullien, the senior author, in 1915 discovered a zoarial hydro- 

 static system in the Anasca. This investigator found that the 

 space under the ectocyst, in certain species lacking a compen- 



colony. Into this space water is introduced or expelled thus com- 

 pensating for the egress and ingress of the polypides. By such 

 means minute creeping zoaria as the Lunulites, e.g., are enabled 

 to maintain themselves on the algas on which live. 



3. In line with their insistance on the value of function it is 

 not siirj)rising that these autliors classify the Tertiary bryozoa 

 on a, pliysioldLri,. rather tliaii a iii<trp}i(»logic basis as is the 

 method foHou,",! I.y th.' (.1«1.t inwst i^ntors. Believing as they 

 do tliat (p. 70) '-111 the bryozoa, as in other living beings, the 

 form is only the result of functions; therefore in the study of 



