Ecliinoderm LarvcB with Two Water-Vascular Systems. 339 



canal is not therefore to be regarded as an attempt on the part of the right 

 side of the larva to form a structure similar to one normally found on the left 

 side, but rather to a precocious beginning of the process of increasing the 

 number of pore-canals such as occurs in all larvae at or after the time of 

 metamorphosis. 



On the other hand I did discover one larva with a right as well as a left 

 pore-canal (fig. 17). But this larva had been classified by me as a " normal " 

 larva, for in all other respects, as, for instance, in its single hydroccele and 

 its well developed pedicellariae, it was entirely normal. The two pore-canals 

 fused with one another in the mid-dorsal line and opened by a median dorsal 

 pore. My results therefore confirm the view of G-emmill that the doubling 

 of the pore-canal and the doubling of the hydroccele are phenomena which 

 are entireh' independent of one another. 



In the majority of the abnormal larvae the right hydroccele is smaller and 

 less advanced in development than the left one. In such cases one or even 

 both of the pedicellariaj proper to the right side may be present (fig. 10). 

 The right hydroccele has thus every appearance of being an after-thought, 

 indiiced by the intervention of an external factor. When it is small it may 

 be entirely devoid of lobes and of an amniotic ca^dty (fig. 11), and even when 

 an amniotic cavity is developed, a disharmony between it and the hydroccele 

 is frequently apparent, for one or more of the lobes of the latter, instead of 

 projecting into the amniotic ca\'ity, may project into the blastocoele {ab.t., 

 fig. 10). In some few cases more than one rudiment of a hydroccele may be 

 formed on the right side ; these cases are due to the splitting of the bud 

 which is formed at the hinder end of the right (or left) anterior coelom. One 

 such specimen was sectioned by me : one of the two right hydrocoeles was 

 normally developed, and had associated with it an amniotic ca^'ity ; the other 

 was a small structure situated posterior to it, and devoid of an amniotic 

 cavity, but possessing well developed lobes. Another specimen was discovered 

 in which the stone-canal alone was doubled on the left side, a phenomenon 

 ob\T.ously to be ascribed to the splitting of the string connecting the 

 hydroccele bud with the anterior coelom {st.c, st."c.," fig. 19). 



B. The ProdvMion of Larvce Devoid of a Hydrocele. 



Tiie converse of a larva developing a hydroccele on both sides would be a 

 larva which developed pedicellarise on both sides. Such larvae are very 

 rare : their significance is discussed later. I have, however, discovered a 

 means of producing larvae devoid both of hydroccele and of pedicellariae, but 

 which possess on both sides in the position usually occupied by the hydroccele 

 a group of spines, and also on both sides a spine or spines in the position 



VOL. xc. — B. . 2 E 



