333 



Hyatt (31). In a later paper, however, he approves the terminology in- 

 troduced, by me, and proposes to call the development of the colony the 

 astogeny (48). 



The embryonic stage of the graptolites is represented by the initial 

 portion of the sicula (first zooid), according to Ruedemann; and Holm 

 (29) asserts that the more pointed end of the sicula "corresponds to the 

 original chitinous covering of the free zooid germ or embryo." This in- 

 itial part of the sicula, according to Ruedemann, holds a position similar 

 to the protoconch of the cephalopod shell. 



In part I of his splendid monograph of the Graptolites (48) of New 

 York, at page 530, Ruedemann says : "It has been pointed out in a former 

 publication that not only did there exist in the graptolites ontogenetic 

 growth stages in the development of the individual zooids, .... 

 but the rhabdosomes in toto and in their parts, the branches, seem also to 

 pass through stages which suggest phylogcnetically preceding forms." 



Of the various ways in which these astogenetic stages express them- 

 selves, Ruedemann mentions the following : "The original direction of 

 growth of the branches of the Dichograptidss has been in the approximate 

 continuation of the sicula, i. e.. an ascending erect position as long as 

 the rhabdosomes were sessile, on the ground. These became pendant when 

 the graptolites attached themselves in a suspended position to seaweeds, 

 as numerous hydroids do today. To restore to the zooids their original 

 . . . . erect position, the branches began now to recurve .... 

 [becoming progressively horizontal, reflexed. reclined and recumbent] 

 . . . . We find now in the majority of the Dichograptiche with the 

 above cited growth directions of the branches, that the latter still retain 

 their original dependent direction, in the proximal parts in some species 

 . . . . while in others by the law of acceleration, the dependent proxi- 

 mal direction has already changed into a horizontal one .... the 

 change in direction becoming progressively more abrupt as the final direc- 

 tion of the branches becomes reclined .... or recumbent 



The branches pass hence, in their development, through different directions 

 representing ontogenetic stages that repeat stations in their phylogenetic 

 development." (48.) 



An analogous fact is found in the character of the thecte. "A com- 

 parison of the form of the theese of the youngest dichograptid genera 

 . . . . with that of the older and presumably phylogenetically preced- 



