ZOOLOGY AND BOTANY, MICROSCOPY, ETC. L51 



the polyp remained attached bo one or mure, and that it began to 

 reconstruct a new calyx around itself. 



One of Gravier's specimens showed six equal groups, separated for 

 almost their entire length, united above by the living tissues. There 

 was no trace of budding. It seems that when the coral reaches a 

 certain size the wall is no longer strong enough to hold together the 

 six segments. These and their living tissues fall apart, and on each of 

 them a new calyx is formed. There is regeneration following longi- 

 tudinal scissiparity — spontaneous division into six segments, and then 

 a reconstruction on the part of each. This is the more remarkable when 

 we note that the living tissues form but a thin layer on the surface 

 of the strongly developed calcareous framework. 



Nerve Conduction in Cassiopea.* — A. G. Mayer finds that the 

 rate of nerve conduction increases as the concentration of the cations 

 of sodium, magnesium, calcium, and potassium decreases. The sodium 

 cation is an active stimulant for nerve- conduction. The magnesium 

 cation is inert and non-toxic ; its role in respect to sodium in sea-water 

 is comparable to that of the nitrogen of the air in relation to oxygen. 

 The effects of potassium are similar to those of sodium, but more 

 marked. These generalizations apply also to the rate at which the 

 motor centres or rhopalia generate stimuli which produce the nerve- 

 impulse, but the rhopalia seem to be more readily affected by osmotic 

 and by concentration* changes than are the nerves. 



In trochophores, ctenophores, and other forms with well-differen- 

 tiated cilia which move in a co-ordinated manner, the normal muscular 

 tonus of the animal produces a state of tension over the outer skin, 

 thus pressing upon the cilia-bearing cells and reducing or even stopping 

 their movement. When the tonus is relieved, however, the cilia beat 

 rapidly. Thus magnesium reduces the muscular tonus and the cilia 

 beat with abnormal activity. Sodium contracts the muscles and stops 

 the cilia. Hence the converse relation between the neuro-muscular and 

 the ciliary movement is a mechanical, not a chemical, matter. 



Law Governing Loss of Weight in Starving Medusse.t — A. G. 

 Mayer has experimented with Cassiopea. xamachana, a Scyphomedusa. 

 When the animal starves the gelatinous mesogloea decreases in volume 

 and apparently serves as the chief store of food. If W be the weight 

 of the medusa when starving begins, a W may represent the decline in 

 weight due to loss of body-substance and of water at the end of the 

 first day, so that at the end of the first day the weight of the medusa is 

 W - a W - W (1 - a). Similarly, at the end of the second day the 

 weight is W (1 - a) - a W (1 - a) = W (1 - a) 2 . Hence the weight y 

 after starving x days is y = W (1 -a) x where a may be called the index 

 of catabolism, the rate of starvation increasing as a increases. 



The medusae were kept in doubly filtered sea-water in diffuse dav- 



* Carnegie Inst. Washington Publications, No. 183 (1914) pp. 25-54 (13 figs.). 

 t Carnegie Inst. Washington Publications, No. 163 (1914) pp. 55-84 (1 pi. and. 

 21 figs.). 



