A NEW EUROPEAN OK IX OH). 



By Austin Hobart Clark, 



Assistant Curator, Division of Marine Invertebrates, U, S. National Museum. 



The careful and painstaking work of the late Dr. Oswald Seeliger 

 upon the embryogeny of Antedon carried on at Trieste gave results 

 which were, in many important particulars, different from those 

 attained by Prof. Jules Barrois at Villafranca and by Mr. II. Bury 

 at Naples. 



Seeliger finds the diameter of the eggs to be 0.25 mm., while 

 Bury gives it as 0.30 mm. It will be remembered that Wyville 

 Thomson found the eggs of Antedon bifida to measure 0.50 mm. in 

 diameter. Seeliger noticed that the segmentation from the third 

 cleavage furrow onward was unequal, resulting in the formation of 

 a blastosphere with markedly larger cells at the vegetative' than at 

 the animal pole, but Bury and Barrois found the cells of the blasto- 

 sphere to be similar throughout. Gastrulation occurred, according 

 to Seeliger, scarcely seven hours after the appearance of the first 

 cleavage furrow; but Barrois and Bury first noticed it from twenty 

 to twenty-four hours after fertilization. Seeliger reports that the 

 blastopore is closed at the latest thirty-six hours after the first 

 cleavage, but Bury records that this change takes place about forty 

 hours after. Bury, who was the first to find underbasals in Antedon 

 (though their occurrence in the larvae had been shown to be probable 

 many years before by Wachsmuth and Springer), gives the usual 

 number as three; Seeliger, on the other baud, reports it as four or live. 



Now from an embryological point of view these differences are 

 fundamental, and are far greater than would reasonably be expected 

 within the limits of a single species. All three workers referred their 

 specimens to Antedon rosa d a , which, as understood by them, ranged 

 from Norway southward to and throughout the Mediterranean; but 

 they all suspected that this specific determination was unsatisfactory, 

 though none of them attempted to investigate the question. The 

 ChalleiKjtr report upon the comatulids had just been published, and 

 this was naturally taken as their systematic hasis. 



In the preparation of a monograph upon the recent crinoids 1 have 

 been enabled, thanks to the kindness of very many fellow-workers, 



Proceedings U. S. National Museum, Vol. 38— No. 1749. 



329 



