ART. 13 BRYOZOAN FAUNA CANU AND BASSLER 21 



Measurements. — 



ha^QM mm. fZs = 0.50-55 mm. 



fA«=0.08mm. fZs = 0.50-55 



Apertiiraj^^^Q QC) ^m. Zooecmm |/^ = o.45 mm. 



Variations. — The micrometric variations are extraordinary; on 

 certain specimens the marginal cells are twice as long as the cells 

 close to the ancestrula. In order to get the average measurement, 

 we have considered a rather large specimen in which all the zooecia 

 were almost of the same dimension. The greatest length observed 

 is 0.65 mm ; the greatest width is 0.70 mm. on the transverse cells. 



The avicularium is not rigorously transverse ; it is a little oblique 

 with the point directed toward the top. In reality it is almost always 

 oriented parallel to the line of junction of two adjacent cells. It is 

 placed to the right or to the left of the cell but always in a fixed 

 portion of the colony. 



Affinities. — In its operculum with two proximal attachments and 

 in its lanceolated mandible this species resembles Microforella coro- 

 nata Audouin, 1826, figured by Waters, 1909. It differs in the arched, 

 hexagonal zooecia, in the presence of a single avicularium placed be- 

 low the ascopore and not of two avicularia placed at the level of the 

 ascopore. These are the only two species provided with this kind of 

 operculum so easily recognized. 



Biology. — This is the most common species in the Galapagos Islands. 

 Its fecundity is very great, as is also the resistance of its larva. The 

 avicularia are the organs of relation in the bryozoa. They are not 

 absolutely necessary to the life of the cell or the colony, but they 

 reveal their habits and their instincts. As the latter are infinitely 

 varied, we can only with difficulty interpret the multiple functions of 

 these minute organs. Here the avicularium is constant in its posi- 

 tion, its direction, and its presence ; it is therefore zooecial, for it is 

 of service to the cell and is indispensable to it. But for what func- 

 tion? It is the more difficult to conceive that in the small locality 

 another species lives ornamented with avicularia absolutely different. 

 The mandible is open and even flattened on the frontal when the 

 tentacles are invaginated. 



The object of the zooecial avicularia appears to be especially to 

 stir the surrounding water and to direct it in a fixed direction. Of 

 little import is the nature of the avicularium employed for this 

 function if the object is attained. Heredity has fixed for each species 

 the form and the advantageous position. 



Our specimens were in reproduction and fixation April 7, 1888. 



Occurrence. — Galapagos Islands, D. 2813. 



Cotypes.—Csii. No. 8492, U.S.N.M. 



