124 SYNOPTIC COLLECTION. 



become purple. Figs. 34 and 35 are ectoderm cells con- 

 taining young spicules ; fig. 34 being not more than one 

 eighth the length of a fully formed spicule. The calcare- 

 ous matter first takes the form of elongated concretions 

 and these like the endodermic spicules are formed by a 

 process of crystallization, as shown by Prof. B. K. 

 Emerson. It is an interesting fact that the development 

 of the spicules in the Alcyonaria is similar to the forma- 

 tion of these hard parts in the mesoderm of sponges, as 

 observed by Schultze and Metschnikoff, and seems not 

 unlike the formation of crystals in vegetable cells, as sug- 

 gested by Wilson. 



It has already been stated that the larva begins to form 

 a colony while it is free. It is probable, as pointed out 

 by Wilson, that the necessity for motion is the cause for 

 the early development of the buds. If the parent after 

 becoming attached had no means of moving, it would 

 doubtless be "smothered in the drifting sand." The 

 position of the first two buds, as seen in fig. 27, is con- 

 stant. The development differs from that of trie parent 

 zoon which has arisen from an egg, so that one ought not 

 to compare egg development with bud development. 

 The young colony takes in water and by means of strong 

 internal currents is able to creep. 



It is instructive to note that an allied genus, Leptogor- 

 gia, does not possess the power of creeping but fastens 

 itself early in life to safe objects, and Dr. Wilson detected 

 no buds at the end of two months. Fig. 36 is a young 

 colony with five pairs o"f buds. In the adult (No. 178, 

 with zoon expanded; No. 179, contracted) the young 

 marginal zoons move the whole colony, and as they 

 mature, become nutritive and reproductive. In time the 

 zoons of this primary group become centers of multiplica- 

 tion and many secondary groups are formed, while com- 

 plexity marks the whole organization. 



The marked bilateral symmetry of Renilla is an evi- 

 dence that the group to which it belongs is more primitive 



