. Echinoidea . It is a remarkable faet that iii souie of the small specimens only oue tubefoot is developed in the piates I. a. i and V. b. i; the posterior tubefoot in these piates must then develop later on. l^'rom the specimen of 3'"'" (Fit;. 16) it appears that the first tubefoot to develop is the inner oue of the piates I. a. I, II. a. i, III. b. i then follows that of the piates I. b. i, II. b. i, III. a. i and the outer tube-foot of the piates I. a. i, II. a. i, III. b. i It is also seen there that the latter appears first in the plate III. b. i. In oue speciuieu I hav
. Echinoidea . It is a remarkable faet that iii souie of the small specimens only oue tubefoot is developed in the piates I. a. i and V. b. i; the posterior tubefoot in these piates must then develop later on. l^'rom the specimen of 3'"'" (Fit;. 16) it appears that the first tubefoot to develop is the inner oue of the piates I. a. I, II. a. i, III. b. i then follows that of the piates I. b. i, II. b. i, III. a. i and the outer tube-foot of the piates I. a. i, II. a. i, III. b. i It is also seen there that the latter appears first in the plate III. b. i. In oue speciuieu I have fouud both tubefeet developed in the plate I. a. I, only oue in V. b. i. — vSouie of the piates in the outer series of the bivial ambulacra may want pores totally; this uiay hold good also for one or two of the piates of the inner series between the proximal ones and those bearing the large subanal tubefeet |the 6th—gth plate). The apical system of the youngest specimen (Fig. 17) is quite in accordauce with that described and figured in the best possible way by Loven for the more advanced stages studied l)v hiui. It is extremely important to learn, how it is in the fullgrowu specimens, as Loven holds its ethmophract> structure to be of very great systematic importance, a view not universally accepted, the numerous transitional stages from an ethmophract to an ethmo- lytic condition Hgured by G au thi er" tending especially to show this feature to be of no primary systematic importance. As shown in Fig. 18 the apical system of the largest specimen is as ethmophract as that of the smallest speci- mens, the madreporic plate does not separate the posterior genital piates. There are four genital pores, with well developed, up to more thau 3'""' long, genital papillæ. A few madreporic pores are fouud also in the left posterior genital plate. The madreporic plate is ofteu somewhat elevated. Fig-18. Apical system of Hcmiastcr expergitits. The spines of the aute
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1900, bookyear1903
