ZOOLOGICAL SOCIETY BULLETIN. 



741 



f-- ■ • _ 



BUGULA TURRITA. A PLUMOSE SPECIES 

 Natural size. Photo by R. C. Osburn. 



2>oia pilosa, described and known as Cyphon- 

 autes. 



By means of this free-swininiinn; larva the 

 distribution of the species is obtained as in other 

 sessile animals. The fresh-water Bruozoa, of 

 which there are only a few species, of wide 

 distribution, have asexual winter buds or gem- 

 mules, known technically as statoblasts, in addi- 

 tion to the sexual reproduction, but the marine 

 forms do not develop statoblasts. A certain 

 amount of distribution in the case of tlie marine 

 species is also brought about by means of drift- 

 ing seaweed and timbers, and species may oc- 

 casionally be transferred over long distances on 

 the bottoms of vessels. How many species thus 

 transported can maintain themselves in their 

 new surroundings is of course problematical, but 

 probably not many of them survive when carried 

 far out of their normal temperature. For ex- 

 ample, the beautiful species, Membranipora 

 tehuelcha, which encrusts the sargassum or 

 gulf weed with a delicate white lace-work, is 

 annualh' carried into the waters of southern 

 New P^ngland, but has never been able to estab- 

 lish itself on our coast. 



When the frec-swiniming larva reaches a cer- 

 tain stage in its development it must become at- 

 tached. If it happens to settle on mud or 

 shifting sand it is lost, but if it is fortunate 

 enough to come in contact with a pebble or 

 shell, seaweed or submerged wood, or the hard 



structure of some other ani- 

 mal, it attaches itself and 

 becomes ]}ermanently locat- 

 ed. It then undergoes a re- 

 markable transformation or 

 metamorphosis, in which all 

 the organs of the larva de- 

 generate and those of the 

 adult develoj). The ances- 

 trula formed by this meta- 

 morpliosis is more simple in 

 structure than the later in- 

 dividuals of the colony, that 

 is, it is not so highly spec- 

 ialized. It is generally pre- 

 sumed to re))resent an earlier 

 stage in the evolution of 

 the zooecium and is there- 

 fore of interest in tracing 

 jiliylogeny. 



The structure of the indi- 

 vidual is fairly simple, but, 

 considering its minute size 

 it is rather complicated. 

 There is a lophophore or 

 peristome, either circular or horseshoe-shaped, 

 surmounted by a crown of tentacles. These are 

 covered with cilia, by the motion of which, the 

 food, consisting of unicellular organisms, is di- 

 rected to the mouth in the center of the lopho- 

 phore. The intestine is a simple U-shaped tube, 

 differentiated into a gullet (in some cases pro- 

 vided with a crushing organ or gizzard), a 

 stomach and an intestine. The vent usually 

 opens outside of the ring of tentacles (group 

 Ectoprocta), but in one small group {Endo- 

 procta) . it opens inside of the tentacle ring. The 

 whole lophophore with tentacles, mouth and 

 anus, may be extended through the aperture of 

 the test or body wall, or it may be withdrawn 

 for protection. The nervous system consists of 

 a single ganglion situated between the mouth 

 and anus, but in spite of the apparent simplicity 

 of the apparatus the animals are highly irritable 

 and very rapid in their movements. 



Surrounding the intestinal tract is a spacious 

 coelom or body cavity, and outside of this is the 

 body wall. The thin living tissue of the bod.v 

 wall is protected by a chitinous or horny layer 

 which is usually further strengthened by a de- 

 posit of lime salts, forming often a remarkably 

 strong, thick shell when fully calcified. This 

 test is usually pitted, cancellated or ribbed in 

 a manner peculiar to the species, and in some 

 forms is perforated by one or more special 

 pores. In some families a membranous area 

 occupies more or less of the front wall of the 



