NO. I3r,5. FRESH- 1 r. I TKll II It 1 'OZO. I — / >. I T 'EXPOn T. 2 1 8 



ponds. The fresh-watei" Biyozoa feed on iiiicroscopic organisms 



whicli tire cauulit in tiio \'oi-tox crcatod ])y thoir ciliated t(Mitacies. 

 Diatoms are especially cons[)icu()Us objects in their alimentary tracts. 

 Since diatoms require lij^-ht for their constructive metabolism, they are 

 found chieHy in the upper strata of the wat(M-, and conseijuently 

 Bryozoa are usually not found at oreat depths. However, in a mass 

 of material dredged liy Prof. H. B. Ward" from the Middle Oround 

 Traverse Bay. Lake ^Michigan, at a depth of 23 to 36 meters. I four.d 

 I^dudivelld clu-enlu'njii and Frcdericella sultana abundant. Although 

 Cristatella is usuall}' found on the under side of floating lily pads 

 or in other situations near the surface, 1 have obtained it from 

 the still waters of Trinity Lake, Westehester Count}-, New York, at 

 a d(^ptli ot" 2 to 3 meters. Asper'^ records dredging Fredericella sid- 

 tana in certain Swiss lakes at a depth of 50 to So meters. Little 

 light penetrates to such a depth, and we ma}' conclude that light is 

 not at all directly necessary for the development of fresh-water 

 liryozoa. Indeed, I have received from Prof. D. S. Hartlin(\ of Blooms- 

 burg, PemisA^hania, masses of Pidml'icdla that were obtained from 

 water pipes where they flourished to an alarming extent. The Br\-- 

 ozoa have become adapted to life in ponds by forming statoldasts at 

 certain seasons of the year. The entire signiticance of the statoblast 

 IS not sufliciently known. Typically, they winter over and one may 

 tind the shores strewn with them in the early spring. They hatch out 

 in New England late in May or early in June. So the statoblasts have 

 come to be regarded as winter buds, or adaptations to preser^•e the 

 race from being killed oft' by freezing of the water. They often begin 

 to develop early in the sunmier and I have observed what has l)cen 

 seen by European ol)servers, that some statol)lasts hatch in nature 

 even in Scptem])er.'' Also Fr.. ^Nliiller has informed Kraepelin' that 

 the fresh-water Bryozoa of Blumenbau, Brazil, which experience no 

 wintei-s, lun'crtheless form statoblasts. It seems fair to conclude that 

 there are other functions performed by the statoblasts than i-esistance 

 to winter. For instanc(\ they serve to maintain the six^cies during 

 drought, or they aid in distri])ution by clinging to the waterfowl or 

 resisting the action of digestive fluids. The Avide distribution of the 

 the species of fresh-water Bryozoa indicates the value of the statoblast 

 in the acc of dispersion. 



METHODS OF PRESERVIXC. 



The chief ditiSculties in the way of preserving fresh-water Bryozoa 

 arise, flrst, from the rapid contraction of the polypid(>s into the corm 

 and, secondly, in the case of the gelatinous forms, from the large 



"Bulletin Michigan Fish Connnisnion, No. fi, ISOti, p. 13. 



i'Zoulogischer Anzeiger, III, 1880, p. 200. 



fBull. Mus. Comp. Zool., XX, 18!»0, p. 102. 



''Kraepeliu, Die Deutschen Siisswasser Bryozoen, 1SS7, }>. sti. 



