28 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 76 



zooecia the avicularia are irregularly disseminated; they are often 

 elliptical and oriented toward the inferior portion of the cells, but 

 frequently there are triangular avicularia with pointed beak oriented 

 toward the superior portion. 



The triangular avicularia are observed ordinarily on the typical 

 form. The large avicularium is characteristic of the variety nitida 

 Hincks, 1881. The aperture and the zooecial form are also those of 

 the same variety. This mixture of characters causes us to doubt the 

 reality of the numerous varieties cited for this proteiform species. 



The cells are oriented in all directions ; this is the celleporine struc 

 ture of Smitt. The species consequently exhibits the development 

 of a colony like a true Cellepore. However, the internal structure 

 is not that of a Cellepore, for the lamellae are very regularly super- 

 posed, the zooecia of one above the other. It should be observed 

 that the irregular orientation of the cells is observed on the colonies 

 of the same form. 



Biology. — The aspect of the large colonies is identical with that of 

 the Cellepores. We have shown (Maroc, p. 54) that the special and 

 irregular development is a special adaptation to a mobile substratum. 

 In Smittina ti^pinosa var. the same phenomena are apparent. The 

 more or less agglomerated sands and pebbles on which the colonies 

 are fixed constitute a substratum without solidity and rigidity, anala- 

 gous to the floating algae. In order to develop, the animal must con- 

 stantly rectify its equilibrium which is compromised unceasingly by 

 causes impossible to foresee or to observe. The disconcerting irregu- 

 larity of the colony is, therefore, quite justified. What are the means 

 employed to assure the equilibrium? The principal ones are the 

 irregularity of budding and the nonorientation of the cells. STnit- 

 tina trispinosa has this property of modifying at will the orientation 

 of the cells, a characteristic very rare in the noncelleporidan Cheilos- 

 tomes. It is not simply by caprice that a normal zooecium engenders 

 an inverse one for it certainly complies with a zoarial necessity. 



The zooecia provided with large avicularia are the ordinary zooecia 

 having the same form, the same irregularity and the same frontal. 

 They are generally a little larger than their neighbors. A third at 

 least of their surface is occupied by the avicularium. The aperture 

 is no longer subterminal but is considerably removed from the distal 

 end. The polypide in order to lodge in the narrow space available 

 must necessarily be dwarfed or twisted abnormally. Anatomic 

 studies by decalcification would be very desirable and would perhaps 

 determine the physiologic action of the large avicularium. The latter 

 is arranged obliquely in such a fashion that it passes above the aper- 

 ture in opening or closing. It is difficult to evaluate the force and 

 efficacy of the movements of the avicularium but as they are ex- 



