186 HIROSHI OHSHIMA 



but continued to lengthen until the hydrocoele reached those 

 invaginations (26, p. 421), As to the nature of these invagina- 

 tions let us examine again (p. 138). 



(g) Posterior Coelom and Genital Stolon. — The 

 anteriorly-prolonged end of the left posterior coelom shares 

 the formation of the echinus-rudiment (Mac Bride, 11, 

 pp. 304-5). This change takes place also on the right side in 

 abnormal larvae where a right hydrocoele developed. In the 

 normal case the genital stolon makes its appearance shortly 

 before metamorphosis from the wall of the left posterior 

 coelom (M a c B r i d e , 11, p. 809). How its right fellow behaves 

 in abnormal larvae is still an open question. Runnstrom 

 inclines to think that in two of his double-hydrocoele larvae 

 (Cases 1 and 2) a rudiment of genital stolon was formed from 

 the right posterior coelom. v. Ubisch (30, p. 445) concludes 

 that the doubleness is not extended to all organs as shown from 

 the fact that in his older double-hydrocoele larva (Case 3) 

 the genital stolon was seen formed only on the left side. This 

 conclusion cannot pass unchallenged because in this larva 

 the right echinus-rudiment was much less advanced than the 

 left, and also because the structure in question is not distinct 

 until the larva reaches the height of its growth. 



(/() Pedicellariae. — In normal Echinus larvae there 

 appear a pair of pedicellariae on the right side, one being 

 dorsal to the loop of the ciliary band, the other ventral to the 

 same. In some imperfectly symmetrical double-hydrocoele 

 larvae one or both of them appear on the right side only 

 (Cases 6, 15, 18) or on both sides of the larva (Mac Bride, 

 15, p. 343). According to Runnstrom the reversed larvae 

 of Strongylocentrotus had pedicellariae appearing on 

 the left side (Cases A and B), and I am inchned to beheve that 

 it is also the case with our Echinus, though unfortunately 

 any positive evidence is lacking at present. In the complete 

 absence of hydrocoele from both sides no true pedicellariae 

 appear (Case 27). Thus the relation between the pedicellariae 

 and echinus-rudiment (or hydrocoele) is somewhat compli- 

 cated. Probably the echinus-rudiment calls forth the forma- 



