127 



nections of the spongy axis of Antcdon worked out with certainty. Al- 

 though Mliller's figure 9, pi. 5, represents the oesophagus (Speiserohre) 

 as situated entirely on one side of the upper end of the spindle, yet it 

 may be, that a portion of the spongy mass, forms a ring around it. In 

 that case it might represent the circular canal of the other echinoderms. 



It is said that the orifice, in the Cystidea and fossil Crinoids, which I 

 believed to have been both oral and anal in function, is anatomically, 

 identical with the anus of the existing Crinoids. If this be true, and if 

 my theory is correct, it must follow that the Cystidea took in their food 

 through the anus. The same phenomenon has been observed in an imma- 

 ture star fish. In the earlier stages of the growth of Astcracanthion 

 hcri/Iinus (Agassiz) a common star fish in the Atlantic. Prof. A. Agassiz 

 finds that there is, at ^first, only a single opening to the digestive 

 sack. This opening is both mouth and anus. Afterwards a second 

 opening is formed which is the permanent mouth. ''The other opening, 

 which was the first to be developed, thus becomes the anus."* This 

 star-fish, therefore, in its embryonic stages takes in its nourishment 

 through the anus. In this respect it is a Cystidean. I am informed 

 that the same arrangement occurs also in the Ophmrians and Echini.. 

 Granting, therefore, that the valvular orifice of the Cystidea is the 

 anatomical homologue of the anal tube of a Fcnfacrinus, it does not follow 

 that it was exclusively anal in its function. I, however, do not admit it 

 to be the homologue of the anus of Pentcicrinus. I heheve it to be the mouth. 



I have stated (ante p. 91) that : — " In this class (the Echinodermata) 

 the position of the various organs, in relation to each other, and also to 

 the general mass of the body, is subject to very great fluctuations." In 

 addition to the few examples of such variations there given, the following 

 may be cited : — 



1. — The aperture which, in an embryonic Echinoderm is both mouth 

 and anus, may, in the mature stage, become the anus only, a new mouth 

 being formed in another part of the body. 



2. — It may become the permanent mouth, and a S3parate anus b'e form- 

 ed in another part. 



3. — The mouth may be, at first, situated out of the centre of the am- 

 bulacral canal system, and afterwards removed to it. 



I believe, that this latter process took place, in the development of the 

 orders Cystidea and Crinoidea. In the first formed or paloeozoic species 

 the mouth was not central, but has become so in the existing types. 



* On the Embryology of Asteracanthion leryllinus, ac, by A. Agassiz. Proc.Am. 

 Acad. Vol. VI., p. 108. 



