474 



SCIENCE 



[N. S. Vol. XLI. No. 1056 



rrom these experiments we conclude that those 

 animals that live in the presence of a great num- 

 ber of bacteria can withstand the action of these 

 bacteria, while those that do not, can not with- 

 stand this action, or that the natural habitat of 

 the animal is the real conditioning factor in its 

 reactions. 



The Bhythmic Pulsation of the Cloaca of Holo- 



thurians: W. J. Ckoziek. 



The cloacal region of pedate holothurians con- 

 tains within itself the mechanism of its coordi- 

 nated pulsation. The isolated cloacal end pulsates 

 rhythmically for many hours after its separation 

 from the rest of the animal, and forms a very 

 simple prepared object with which to investigate 

 phenomena of rhythmic movement. The rate of 

 pulsation of the isolated cloacal extremity of 

 Stichopus mcebU was found to have a temperature 

 coefficient of about 2.4; it was capable of long 

 continuance in water practically free from dis- 

 solved oxygen. The coordinating mechanism was 

 much more powerfully affected by nicotine and 

 atropine than by cocaine or morphine. The dura- 

 tion of pulsation and of irritability to mechanical 

 stimulation in diluted sea water was proportional 

 to about the square of the concentration. The 

 alkaline chlorides preserved pulsation and irrita- 

 bility in the order: 



NaCl > LiCl > NH,OK > KCl . MgSO. 



was a more powerful depressant than isomolecular 

 or (Mg-) isionic MgCL. Each one of the salts of 

 sea water was necessary for the continuance of 

 pulsation; this was notably true of MgSO,, which 

 led to normal relaxation after systole. Alteration 

 of the Ch. from pn^^S.O (normal) to p h = 6.0 

 was sufficient to produce stoppage of pulsation 

 within 5 minutes. The brownish skin pigment 

 was given out under abnormal ionic or osmotic 

 conditions, and afforded some index of permeabil- 

 ity changes. 



Bcology 

 Altitudinal Distribiition of PlanJcton Crustacea in 



Colorado: O. S. Dodds. 



In 284 collections from 124 lakes and ponds, at 

 elevations between 4,100 and 12,188 feet, the au- 

 thor found 50 species of Entomostraca. Other 

 records raise the list to 69 species (Phyllopoda 

 14, Cladoeera 35, Copepoda 20). There are 22 

 species confined to the mountains, 27 found only 

 in the plains, and 20 range more or less widely 

 through both areas. More definitely, there may be 

 recognized four zones, marked more or less clearly 



by physiographic, climatic and faunal characters, 

 as follows: Plains Zone, up to 5,400 feet; Foot- 

 hill Zone, 5,400 to 8,500 feet; Montane Zone, 

 8,500 to 11,000 feet; Alpine Zone, above 11,000 

 feet. In determining distribution of species and 

 boundaries of zones, temperature seems to be the 

 most important factor. 



In climate and fauna, these zones have their 

 nearest geographical equivalents as follows: Al- 

 pine zone to Labrador, southern Greenland and 

 extreme north of Eussia; Montane and Foothill 

 zones to the region north of Lake Superior, New- 

 foundland, and the main part of Norway and 

 Sweden. The plains zone to the Mississippi val- 

 ley and the lowlands of Europe, except that the 

 semi-arid climate gives some specialized features. 

 The Land and Fresh-water Crustacea of Co- 

 lombia: A. S. Pearse. (Lantern slides.) 

 The Vertical Distribution of Some PlanMon 



Protozoa in Wisconsin Lalces: Chancey Jtjday. 

 An Experimental Transmission of Sarcocystis 



Tenella: John W. Scott. 

 Exceptional Life-histories Among the TJnionidce: 



Arthur D. Howard. 



Glochidia of a fresh -water mussel (XJnionidEe) 

 were found upon the external gills of Necturus 

 maculosus. Eighty per cent, of the collections 

 from the Mississippi were infected. By keeping 

 the neeturus alive from October to May the larval 

 mussels were carried through the metamorphosis. 

 The species was still unknown, as it did not cor- 

 respond with any of the collection of glochidia 

 available and which was supposed to be complete 

 for the region. Study of the ranges of all re- 

 ported forms revealed one rare species, Hemilas- 

 tena ambigua Say, which might be the adult de- 

 sired. Gravid mussels containing glochidia were 

 found after considerable search late in September 

 and a comparison with the glochidia in question 

 removed all doubt that they were of the same 

 species. The mussel has the unusual habit of liv- 

 ing under flat stones of the flag-stone type. As 

 Necturus is known to frequently seek such shelter, 

 the manner of infection is explained. 



Anodonta imhecillis has been reported by Sterki 

 as normally hermaphroditic and by Howard as 

 non-parasitic. The embryos have been observed 

 within the egg-membrane up to the attainment of 

 the juvenile stage. They were found to escape 

 from the parental marsupium in late spring and 

 their development followed to a growth of shell 

 many times that of the original glochidium. Ob- 

 servations of the degree of development at various 



