DESCRIPTION 31 



under the direction of Dr. Ralph I. Smith of the Univ. of Cahfornia. 

 The plates of 72 animals were counted by members of the class, and 

 there seems no doubt that the number of plates varies with the size 

 of the animal. Jackson (1927, p. 471) states that the increase in size 

 in Arbacia is attained more by the increase in size of individual plates 

 than by increase in number; an animal 4.7 cm. in diameter had 16 

 plates in an interambulacrum, and one 1.4 cm. had 10 plates. A care- 

 ful study of three Chinese (and Japanese) species, Temnopleurus toreu- 

 maticus, T. hardwickii and Strongylocentrotus pulcherrimus, by Hsai (1948) 

 collected from Kiao-chow Bay, Tsingtao, showed that in young animals 

 the number of plates is a function of the diameter of the test, but that 

 as the animals approach maximal size, they stop forming new plates 

 and growth takes place only by the enlargement of the plates. Many 

 years ago, the celebrated naturalist Forbes (1841) estimated that in 

 Echinus esculentus, a much larger form than Arbacia, there are in an 

 animal of moderate size 600 plates, 3,720 pores, 1,860 suckers and 

 4,000 spines. 



There is a simple coiled alimentary canal, a water vascular system 

 and a nervous system, but the main body of the animal (in season) is 

 filled with the five ovaries or testes (Fig. 7). The ovaries are red, or 

 brownish late in the season, and the testes are brownish white, the 

 oozing sperm being white. The histological structure of the gonads and 

 gonad walls of A. punctulata is described with drawings and photo- 

 graphs by L. Palmer (1937) and L. Palmer Wilson (1940). A photo- 

 graph of the ovary is given by Liebman (1950). In other species, the 

 genital glands have been described by R. Koehler (1883) for A. lixula 

 and many other species; by Hamman (1887) for many species; by 

 Tennent, Gardiner, and Smith (1931) and Miller and Smith (1931) 

 for Echinometra lucunter ; by Lindahl (1932 b) for Paracentrotus lividus ; 

 by Aiyar (1938) for the Indian species, Salmacis bicolor ; and by Tennent 

 and Ito (1941) for the Japanese species, Mespilia globulus. 



An excellent account of the structure of A. punctulata is given by 

 Reid in Brown's Selected Invertebrate Types (1950), written for the In- 

 vertebrate Zoology course at Woods Hole (Figs. 6, 7). Other accounts 

 of ^. punctulata are those of: A. Agassiz (1872-1874) Revision of the 

 Echini (pp. 263-266) ; H. L. Clark (1902) Echinoderms of the Woods Hole 

 Region, p. 563; Coe (1912) Echinoderms of Connecticut, pp. 85-108; Jack- 

 son (1912) Phylogeny of the Echini, (1927) Studies of Arbacia punctulata and 

 Allies (external structure) ; Petrunkewitch (1916) Morphology of Inverte- 

 brate Types, pp. 1 9 1-20 1. W. K. Brooks (1882) in his Handbook of Inver- 

 tebrate ^oology describes and gives good drawings of the external and 



