THE DEVELOPMENT OP ASTEEINA GIBBOSA. 251 



divided into distinct rounded lobes lined by cylindrical epi- 

 thelium {rhy.), in all respects similar to those of the left, and 

 the rudiment opens by a narrow but distinct slit into the 

 anterior coelom. This larva also exhibits another very common 

 abnormality, which I do not in the least understand ; this con- 

 sists of the breaking up of the gut epithelium into a mass of 

 cells having the appearance of mesenchyme, which choke up 

 the lumen, but leave the walls almost denuded of epithelium, 

 consisting chiefly of the basement membrane. This curious 

 change can take place at any stage from the commencement of 

 the differentiation of the ccelom, up to young adults a month 

 old : in one such specimen it affected the pyloric caeca. As to 

 what its meaning is, I confess I am entirely in the dark. 



Figs. 87 and 88 represent a most remarkable larva. The 

 development of the left posterior coelom would indicate that it 

 had reached Stage E, but the left hydrocoele consists only of 

 four lobes, and is poorly developed. There are two rudiments 

 of a hydrocoele on the right side ; the more ventral has three 

 distinct lobes lined by cylindrical epithelium {/hy'., fig. 88), 

 and opens by a distinct opening into the anterior coelom ; the 

 more dorsal is perfectly normal (rhy., fig. 87) ; but, as if 

 to emphasise the fact that, in spite of the presence of the 

 other rudiment, it does in fact represent a hydrocoele, we find 

 in connection with it a second small stone-canal and pore- 

 canal {p'&. sf. c). The relation of these to the right hydro- 

 coele may seem unusual ; instead of the canal (conjoined stone 

 and pore-canal) leading from the hydrocoele to the anterior 

 coelom and thence to the exterior, it appears to lead from the 

 anterior coelom to the hydrocoele and thence to the exterior. 

 This apparent difference may be reconciled with the arrange- 

 ment on the left side by observing the angle which stone- 

 canal and pore-canal make with one another. Woodcut 3, p. 

 253, shows that this is an acute instead of an obtuse angle, and 

 hence that stone-canal and pore-canal have coalesced laterally ; 

 Woodcut 2 shows for the sake of comparison the normal stone- 

 canal and pore-canal and their relationship to the left hydro- 

 coele and the axial sinus or anterior ccelom. 



