ECIIINUIDHA. II. QQ 



It is a remarkable fact lliat in sour- oi the Muall specimens only one tiil)efoot is developed in 

 the plates I. a. i and V. b. i; the posterior tubefoot in these i)lates must then develop later on. Ihoni 

 the .speeimen of 3""" {Fu^. 16) it appears tliat the first tnl)efoot to develop is the inner one of the 



plates I. a. I, II. a. i, III. b. i then follows that of the plates I. b. i, II. b. i, Ill.a. i and lastly 



the onter tube-foot of the plates I. a. i, II. a. i, III. b. 1 It is al.so .seen there that the latter 



appears first in the plate III. b. i. In one si)ecimen I have fomul both tubefcet developed in the plate 

 I. a. I, only one in V. b. i. — • Some of tlie plates in the outer series of the bivial ambulacra may want 

 pores {otally; this may hold good also for one or two of the plates of the inner series between the 

 proximal ones and those bearing the large snbanal tubefeet (the 6th gth plate). 



The apical system of the youngest .specimen (Fig. 17) is quite in accordance with that described 

 and figured in the best possible way by Loven for the more advanced stages studied by him. It is 

 extremely important to learn, how it is in the fullgrown specimen.s, as Loven holds its . cthmophract'> 

 structure to be of very great systematic importance, a v'iew not universalh- 

 accepted, the numerous transitional stages from an cthmophract to an ethmo- 

 lytic condition figured b\' Ciauthier' tending esi)ecially to show this feature 

 to be of no primary systematic importance. As shown in Fig. iS the apical 

 system of the largest specimen is as ethmophract as that of the smallest speci- 

 mens, the madreporic plate does not sej^arate the posterior genital plates. 

 There are four genital pores, with well developed, up to more than 3""" long, 

 genital papillae. A few madreporic pores are found also in the left posterior 



genital plate. The madreporic plate is often somewhat elevated. Fig- 18. Apical .system of 



r^, ■ r ,1 ■ 1 r 1 , i-i Hciuiaster expereilus. 



The spmes of the anterior end of the test are somewhat spearshaped, „„„ ;„ \^^^„^ 



with coarsely serrate edge, in side-view curved and quite sharp. (PI. XV. Fig. 44). ^ 



Those on the posterior end of the test are more spoonshaped, with smooth edge; the spines of the 



sides of the test are intermediate in shape between these two forms. The spines of the actinal plastron 



(PI. XV. Fig. 50) are much widened in the point-, the widened part being sometimes almost quite 



hyaline, almost without any reticulate tissue in the middle; in others the reticulate tissue has a 



greater extent, both kinds occurring together in the same specimen. It is worth noticing that in the 



specimen of 3""" length these spines are already of the t)'pical form. The spines within the fasciole are 



more or less spoon-shaped; those along the anterior ambulacrum increase in length towards the apical 



system, the uppermost being the longest, reaching even beyond the fasciole behind (not widened in 



the point). The size of the tubercles is, of course, in accordance with this fact, as is seen in Loven's 



Fig. 115. The small miliary spines are mainly of the same structure as the clavulte. (Comp. Agassiz 



■ Recherches sur I'appareil apical dans quelques especes d'Echiuides appartenant au genre <tHemiaster». Assoc. Franc, 

 pour I'avancement des Sciences. 18S6. It is especially to be remarked that in a single species, Hemiaster bainettsis, Gauthier 

 finds all stages represented from a typical ethmophract apical sj-stem in the ^oung specimens to an ethmolytic in the large 

 specimens. (Comp. also: Lambert. Note sur le developpement de I'Echinospatangus neocomiensis d'Orbigny. Bull. See. Yonne. 

 i88g. p. II. Note; De Loriol. Notes pour servir a I'etude des Echinodermes. VI. Rev. Suisse de Zool. V. 1897. p. 175; 

 A. Valette. Description de quelques Echinides nouveaux. Bull. Soc. Yonne. 1905. p. 44). 



2 In the Blake -Echini p. 67 Professor Agassiz says of these spines in the young II.Mcntsi: ^The outer slie.ith of 

 calcareous rods becomes solidified as thin lamellse, forming in one case in the primary interanibulacral spines of the anterior 



part of the test on the abactinal side, above the ambitus, a spearlike head to the shaft of the radioles; in the shorter 



radioles of the actinal plastron the lamella; all develop into this spoon-shaped extremity >. — Only two of the lamellae develop 

 in this manner, the rest of them disappear on the lower part of the head. 



13* 



