AUTHOR S ABSTRACT OP THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE SEPTEMBER. 



THE EARLY DEVELOPMENT OF A STARFISH, MATERIA 

 (ASTERINA) MINEATA 



HAROLD HEATH 



Frovi the Leland Stanford Junior University, California 



FI\E FIGURES 



During the past summer a small number of gastrulae were dis- 

 covered in the plankton of Monterey Bay, California, which 

 exhibited a unique combination of characters, relating them on 

 one hand to the Echinodermata and on the other to the Enterop- 

 neusta. To discover their true relationship all were placed in 

 balanced aquaria where they subsequently developed into bi- 

 pinnariae. Ova of various species of shore-dwelling starfishes 

 were then artificially fertilized and reared for a sufficient length 

 of time to show that the first captured specimens were the 

 young of Pateria (Asterina) mineata. 



Judging from artificially fertihzed material the segmentation 

 and early blastula stages do not exhibit any especially note- 

 worthy features, but beyond this point certain structures arise 

 that have no known counterpart among starfishes. The first 

 of these unique organs is the apical plate. In the late blastula 

 stage the cells about the animal pole commence to elongate 

 and, in the gastrula, form a thickened area, more or less lens- 

 shaped in form, having approximately one half the diameter of 

 the transverse axis of the embryo. As indicated in the drawings 

 (figs. 3, 5) its center is exactly opposite to the blastopore and 

 therefore is strictly apical. 



Sections show the component cells to possess a height fully 

 tKree times that of the average ectoderm cell of the animal half 

 of the embryo. Passing outwardly the altitude diminishes at a 

 fairly uniform rate until the outer hmits are reached. The 

 nuclei are distally located and therefore similar in this respect 



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JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2 



