No. 4. — Studies from the Newport Marine Zoological Laboratory. 

 Communicated hy Alexander Agassiz. 



XVIII. 



On the Deoelopment of the Calcareous Plates of Amphiura. 

 By J. Walter Fewkes. 



In a paper published in March, 1886,* it was shown that the egg of 

 Ophiopholis develops into a pluteus-like larva in which the two lateral 

 arms with calcareous rods are well developed. In the month of July 

 of the past summer a similar larva was traced into an adult pluteus. 

 This adult pluteus of Ophiopholis is the same as that doubtfully referred 

 by A. Agassiz to Amphiura squamata, thus confirming the statements f 

 made in the paper above quoted. While however it was possible to 

 determine the general anatomy of the adult pluteus of Ophiopholis, cir- 

 cumstances rendered it impossible for me to follow the growth of the 

 calcareous plates and skeleton in the body of the young Ophiopholis 

 forming in this pluteus. It was more convenient to complete my studies 

 of this part of the subject on another genus. For this work the well- 

 known viviparous Ophiuran, Amphiura squamata, Sars, was chosen. 



This species is well suited for the study. It is common near the New- 

 port Marine Laboratory, and easily collected. It is viviparous, and the 

 young are found in the parents through the months of August and Sep- 

 tember, when the Laboratory is open for work. Whatever disadvan- 

 tages come from the possible retardation or acceleration in the sequence 

 of the development of the plates brought about by the abbreviated 

 development, is certainly offset by the ease with which material can be 



* Preliminary Observations on the Development of Ophiopholis and Echina- 

 rachnius, Bull. Mus. Comp. Zobl., Vol. XIL No. 4, pp. 105-119. In this paper it was 

 first shown that Ophiopholis has a nomadic pluteus. 



t On p. 119 (op. cit.) it is said, " Ophiopholis aculeata has a developnient with 

 metamorphosis, passing through a larval stage called the pluteus," and on p. 106, 

 note, " The pluteus referred to Amphiura squamata in the ' Embryology of the Echi- 

 noderms,' and doubtfully to Amphiura in ' Embryological Monographs,' may be a 

 pluteus of Ophiopholis." The embryology of A. squamata is partially traced in the 

 following pages. 



VOL. XIII. — NO. 4. 



