156 Mr. E. Billings on the Structure of 



from time to time, thrown out through the mouth, just as a 

 starfish or a zoophyte frees itself of the refuse portions of its food, 

 by casting it out of the same aperture through which it entered. 



10. On the Theory that the Amhulacral and Ovarian Orifices 

 are the Oral Apertures. 



Assuming that the four objections above noticed are suffi- 

 cient to prove that the aperture which I call the mouth is not 

 that organ, it is contended that the Cystidea, Blastoidea, and 

 PalfBOcrinoidea ingested their food through their ambulacral 

 and ovarian orifices. This appears to me in the highest degree 

 improbable. In the recent Crinoids the grooves of the arms 

 are occupied by four sets of tubes, which Dr. Carpenter calls 

 the coeliac, the subtentacular, the ovarian, and the tentacular 

 canals. None of them communicate with the stomach. It is 

 impossible that the most minute particle of food could gain 

 access to the interior of the animal through any of them. 

 The structure of the arms of the palaeozoic Crinoids is such 

 that we must presume that their grooves were occupied by 

 similar tubes, which passed through the ambulacral orifices 

 into the perivisceral space. In the Cystidea and Blastoidea 

 the respiratory organs were not situated in the grooves of the 

 arms, and the ambulacral orifices were therefore only ovarian 

 in their function. The improbability of their being also oral 

 apertures is best shown by an illustration. 



In fig. 13 is represented (natural size) the apertures of the 

 smallest specimen of Caryocrinus ornatus -p. ,0 -p- I/1 

 in our collection, selected for the present ^^' ' ^°* 



purpose because in the young of this spe- 

 cies the valvular orifice is larger in pro- 

 portion to the size of the disk than it is in 

 the adult. It is in this specimen about 

 one third of the whole width of the apical disk, while in a full- 

 grown Caryocrinus it is only one ninth of the width. The 

 same proportional size of the mouth according to age occurs in 

 Antedon rosaceus. The valvular mouth at first is as wide as 

 the disk ; but as the age of the animal increases, the disk 

 grows wider, but the mouth does not. The ovarian pores in 

 Caryocrinus, however, are as large in the small ones (once 

 they make their appearance) as they are in those full-grown. 

 For recognizing these as ovarian pores we have the following 

 reasons : — 1, they are situated at the bases of the arms where 

 the ovarian tubes must pass from the grooves into the peri- 

 visceral cavity ; 2, when compared with the ovarian pores 

 of a sea-urchin, they have the same size, form, and aspect. 

 Fig. 14 represents the ovarian pores of the sea-urchin Toxo- 



