FORM AND LIFE. 529 



bell ; later, it took a strange shape, which was not inappropriately 

 compared to a lectern. M. Chabry even designated it by the Latin 

 name pluteus, which means pulpit. As the time for this change 

 of form approaches, there can be seen appearing in the tissues of 

 the young larva a kind of calcareous needles, called spicules, the 

 form and disposition of which are identical in all individuals of 

 the same species. These spicules are composed of the carbonate 

 of lime which the larva finds in the sea water, and which it ab- 

 sorbs as the roots of a plant absorb the potash contained in the 

 soil. This lime traverses the tissues of the larva and collects for 

 a time in them before settling in the half-crystalline figure of the 

 spicules. It may be remarked that although they present a regu- 

 lar arrangement in the larva, the spicules have no relation, at least 

 in the beginning, with the external form or the shape of the organs 

 of the animal. 



M. Chabry asked what would happen if he tried by raising the 

 larvae in water destitute of lime to prevent the formation of the 

 spicules. The experiment was not without difficulties. It was 

 necessary to prepare artificially a limeless sea water. With all 

 the pains M. Chabry could take, in the light of the best analysis, 

 the larvse perished in the artificial water as soon as they were 

 hatched. He then tried diminishing by degrees the proportion of 

 lime in the natural water. This lime was the sulphate, and the 

 experiment was directed, in order to prevent too radically chang- 

 ing the water, to substituting another base for calcium. Sodium 

 was taken, because, it being already very abundant in the water, 

 the slight addition of it which it would be necessary to make to 

 replace the lime could not have any great influence. The results 

 were very plain. Without any mixture of lime in the water, the 

 just-hatched larvae were arrested in their development and died in 

 a few hours. If the elimination of calcium is not pushed to its 

 extreme limits, and only a fifteenth part of the already very slight 

 quantity contained in sea water is left, the larvse will not be for 

 forty hours distinguishable from those which are developed in 

 normal water. At the end of that time the spicules should appear 

 while the larva is assuming the form of the pluteus. But in water 

 containing only a fifteenth of the normal calcium this change is 

 not effected. Twenty hours later, in the sixtieth hour of their 

 lives, the larvae are still in the same condition, while those in nor- 

 mal water have spicules already branched, and their having taken 

 the form of the pluteus is marked both by their shape and by the 

 division of their intestine into distinct regions. The larvae de- 

 prived of lime first exhibit this modification of the intestine toward 

 the ninetieth hour, but they have no spicules and have not become 

 pluteus. Their external form has therefore been profoundly af- 

 fected by some change that has been introduced into the inner 



VOL. XLV. 41 



