MUSEUM OF COMPARATIVE ZOOLOGY. 37 



(Odontophore) First Interbrachials. Oral. 



Other Interbrachials. 



Connectives. "Wanting on arms. 



Terminals. Terminals. 



Dorsals. Dorsals. 



Dorsolateral. Wanting. 



Marginal* Wanting. 



Ambulacrals. Ambulacrals. 



Interambulacrals.t Laterals (Adambulacrals). 



Under-basals ? Under-basals. 



The ventrals of Amphiura and the plates of the stone canal and pedi- 

 cellarise of Asterias are not common to the two genera. 



Spines (embryonic) are present in the laterals (adambulacrals) of 

 Amphiura. They are not found in the ambulacral rafters of Asterias. 



It will be noticed in the above list, that two adambulacrals of Am- 

 phiura (1 and 2) are designated as the same as interbrachial ends of the 

 oral ambulacrals of Asterias. In Asterias they resemble other ambula- 

 crals, except that on their interradial ends they bear spines, while in 

 Amphiura they more closely resemble adambulacrals, and so they were 

 called by Ludwig. It will probably be said, that they are either ambu- 

 lacral or interambulacral (adambulacral), and abler persons than myself 

 may be able to show that the oral ambulacrals of Asterias are different 

 from the oral adambulacrals of Amphiura. I confess, however, that I 

 am unable to see that they may not be the same plates, now modified 

 in one way, now in another. They are the most difficult plates to com- 

 pare of any in Asterias and Amphiura. Without being able to make up 

 my mind whether or not there are plates in the young starfish homolo- 

 gous with the torus and teeth of Amphiura, I think it not improbable 

 that these structures may be homologous with the "Aristotle's Lantern" 

 of urchins, but I am not willing yet to venture that statement. There 

 are in certain genera of Asteroids, of course, teeth which may be com- 

 pared with the teeth of the Amphiura ; but whether they are homolo- 

 gous is doubtful. 



P. Herbert Carpenter, in his paper on the growth of the calcareous 

 plates of Amphiura, has pointed out differences in the time of appear- 

 ance of the same plates in the American and European varieties of 

 'A. squamata. I regard this as a very fruitful field for morphological 

 study. The recognition of a great difference in the time of the appear- 

 ance of homologous plates among Echinoderms seems to me an impor- 

 tant one. There is considerable variation in the time and sequence of 



* Interambulacral of some authors. I Adambulacrals of recent authors. 



