SECT. n. INTERMEDIATE SKELETON. 43 



and sends out many cylindrical, but more generally 

 club-shaped spines in all directions, though they usually 

 affect more or less that of the equator, as in the 

 typical form Calcarina calcar, which is exactly like the 

 rowel of a spur. The spines are for the most part 

 thick and clumsy, and give the shell a very uncouth 

 appearance, especially when their extremities are forked. 

 The turbinoid spire of the shell has a globose centre 

 surrounded by about five whorls progressively increasing 

 in size, and divided by perforated septa into chambers. 

 Each whorl is merely applied to that preceding it, and 

 does not invest it in the least degree. Internally the 

 turns of the spire are separated from each other by 

 the interposition of a solid layer of shell-substance quite 

 distinct from the walls of the chambers. A crystalline 

 deposit begins at the very centre of the spire in a thin 

 layer gradually increasing in thickness as it proceeds, 

 and sending off club-shaped spines from time to time 

 so that the spines are of later and later production, and 

 become thicker and longer. From this it is evident that 

 the intermediate skeleton grows simultaneously with 

 the turns of the spire, but strange as it may seem, their 

 growth is independent, though both are nourished and 

 increased by the sarcode in the interior of the chambers. 

 For the intermediate skeleton is traversed in every part 

 by an elongated network of canals, which begin from 

 irregular lacunae or openings in the walls of the cham- 

 bers, and extend to the extremities of the spines. 

 Through these canals threads of the sarcode body of 

 the animal within the chambers have access to the 

 exterior, and provide nourishment for the intermediate 

 skeleton; while pseudopodia, passing into the water 

 through pores in the last partition of the shell, provide 

 for its growth and procure nourishment for the animal. 

 The communication between the adjacent chambers 

 in the whorls, is by means of a series of pores in the 



