Bd. VI: 4) THE ECHINOIDEA. 79 



be observed on the abactinal side is that the odd posterior interambulacrum has 

 pushed its way forwards along the sides of the periproct, three small plates having 

 developed here on either side. The periproct, in which the plate at the posterior 

 edge, the supposed genital 5, is to be especially noticed, still directly joins the madre- 

 porite, which has as yet only one pore. In the odd anterior ambulacrum 4—5 pairs 

 of pores have appeared, and they are already double, except the inner ones. In the 

 paired ambulacra no pores have appeared as yet. The mouth has not yet been 

 formed; some small plates have appeared in the actinal membrane. The peristome 

 is round. The fasciole is still in the primitive condition, enclosing both the apical 

 system and the periproct. On the madreporite some small tubercles have appeared 

 which might well seem to represent the beginning of the transverse band of the 

 fasciole. This is, however, not the case, as is easily seen by a careful comparison 

 with the following stages. While the tubercles of the madreporite remain distinct 

 until much later stages, the transverse band of the fasciole appears behind the madre- 

 porite, traversing the upper plates of the posterior interambulacrum (Fig. 19). The 

 tubercles on the madreporite are also slightly larger than those of the fasciole, and 

 the spines borne on them differ distinctly in structure from the clavulas of the 

 fasciole, being smooth and only slightly widened in the point, while the clavulse are 

 much widened in the point and thorny on the shaft. (In the grown specimens both 

 kinds are thorny on the shaft.) 



In the PI. XX. a. Fig. 9. of the »Challenger> Echinoidea is represented an ex- 

 actly corresponding stage of a young A. cordatus {yHemiaster cavernosus^)\ it is 

 reproduced somewhat diagrammatically in the »Panamic Deep Sea Echini» Fig. 306, 

 p. 212. * The original figure is in many respects inaccurate and does not give the 

 limits of the plates; in the reproduction of the figure the limits of the plates have 

 been introduced, but evidently without reexamination of the specimen — and the 

 result has not been very satisfactory. The ambulacra are represented as having each 

 one or two large pores; in reality the frontal ambulacrum has already 5 pairs of 

 ambulacral plates with distinct, double pores inside the fasciole, while the paired 

 ambulacra have no pores at all inside (or in) the fasciole; only the ocular pore and 

 the terminal tentacle are large and distinct — but this pore is not represented in the 

 quoted figure in the two left ambulacra. That the tubercles within the fasciole are 

 represented too large — ■ they do not exceed those outside the fasciole in size — is 

 of minor importance. But the facts pointed out here bear evidence that this figure 

 is quite a misconception, the original and the altered copy as well; it ought not to 



* In the »Challenger» Echinoidea p. 181 it is described as having the periproct ^covered by a large 

 plate having a small opening opposite to the left posterior ambulacrum* . This is evidently due to a mis- 

 conception, the madreporite having been taken for the anal area and vice versa. (Cf. Die Echinoiden d. 

 deutschen Siidpolar-Exped. p. 89.) In the reproduction of the figure in the »Panamic Deep Sea Echini* 

 this error has been corrected. 



