PHOEMOSOMA HISPIDUM. 95 



bulacral plates ; they now arise, even in the specimen 120 mm. in diameter, 

 from the flanks of the ocular plates and not from the genitals (PI. .39, 

 fig. l). In the older specimen (PI. 39, fig. 2) the intrusion of the anal 

 plates within the interambulacral area has greatly disturbed the regular 

 arrangement of the older plates ami the mode of growth of the new plates. 

 In the specimen of 130 mm. (PI. 39, fig. ;?) bare spaces in addition to those in 

 continuation of the genital plates have developed so as to separate the 

 madreporic genital 1 from the odd anterior ocular, the left anterior and left 

 posterior oculars from the adjoining interambulacral zone. The right 

 posterior ocular is separated from the adjoining interambulacrum so that 

 one of the intercalated anal plates occupies the position of a newly formed 

 interambulacral plate (PI. 39, fig. .'). 



When we examine the apical system of the largest specimen collected, 

 203 mm. in diameter (PI. 39, fig. •-'), we find the narrow elongated triangular 

 extension of the membraneous part of the genitals extending along the 

 median interambulacral line as far as the fourth plate, so that the abactinal 

 parts of the interambulacral zones are wideh/ separated. As in the speci- 

 men of 130 mm. (PI. 39, fig. ..'), bare membraneous spaces occur between 

 many of the anal plates in the anterior part of the apical system, on the 

 anal side of the anterior genital plates, of the odd posterior genital and the 

 right posterior ocular plate. The madreporic genital is joined with the odd 

 anterior ocular plate; the madreporite occupies only the madreporic genital, 

 which is polygonal and much larger than any other genital. In fact, the 

 other genitals, with the exception of the left anterior one, have lost their 

 great size as compared to that of the anal plates. Many of the latter are 

 now nearly as large as the former, carrying secondaries and miliaries. 

 Otherwise all the genitals and oculars are widely separated, the inter- 

 calated anal plates abutting on the abactinal part of each of the two inter- 

 ambulacral zones to such an extent that in some interambulacra it is almost 

 impossible to determine which is the terminal interambulacral plate or 

 the intercalated anal plate. 



It is this extraordinary change in the anal system which I had observed 

 in the abactinal part of the test, which has prompted Dr. Mortensen 2 to 

 credit me with the most extraordinary ignorance of the rudimentary embryo- 

 logical data, many of which I was the first to discover. That this remark- 

 able intercalation exists there is not the least doubt, and it naturally suggests 



1 The madreporite extends over one of the adjoining anal plates. - Mortensen, 1. c. p. 175. 



