Notes on eoAinodeem MoupaoLooY, 385 



genital glands. But when the glands are short, and do not 

 extend over more than three or four pinnule segments, the 

 distal ends of the genital pinnules are often abundantly pro- 

 vided with sacculij although there are few or none in their 

 enlarged basal portions. I do not know how this will be 

 explained by the supporters of the algal nature of the sacculi, 

 and their relations in Antedon-species with plated ambulacra 

 present still greater difficulties. I have sometimes failed to 

 find them, even in Antedon, among the various plates sur- 

 rounding the ambulacra ; but, as a general rule, they are fairly 

 well developed in the pinnules, and occupy an extremely con- 

 stant position with regard to the ambulacral plates. In those 

 species which have the most highly differentiated pinnule- 

 ambulacra the sacculi alternate with the tentacular groups, 

 just as in Antedon rosacea, and the distal edges of the side 

 plates are notched for their reception in the most regular way 

 possible (Fig. 1, s). It does not appear probable to me that the 

 calcareous elements of the skeleton would be so regularly 

 modified for the reception of the sacculi if these structures 

 were merely vegetable parasites ; and the difficulties inherent 

 in this view of their origin are increased by the fact that the 

 side plates of Hyocriuus, Pentacrinus, and Metacrinus 

 are not notched for the reception of sacculi, which do not occur 

 at all in these genera, even when they are living side by side 

 with Antedons in which sacculi are abundantly distributed 

 at the sides of the pinnule-ambulacra. 



Sacculi occur in nearly all the species of Antedon, in 

 Promachocrinus, Atelecrinus, and in three species of 

 Eudiocrinus, though they are absent in the other two. 

 They are sometimes to be found in Rhizocrinus and Bathy- 

 crinus, though they are often so small and undeveloped as to 

 be barely recognisable ; but I have failed altogether to find 

 them in Actinometra, Holopus, Hyocrinus, Meta- 

 crinus, or Pentacrinus,^ even when these genera have 



1 The structures which I formerly regarded as imperfect sacculi in Penta- 

 crinus, so far as I could judge from the surface characters only, turn out to 

 be of a different nature when seen in thin sections. 



