SERTULARIA. 181 



move ; and the whole, not under 150, collecting towards one part of their 

 new habitation, then remained quiescent. Fifteen or sixteen days subse- 

 quent to their departure from the vesicles, their colour remained as vivid 

 as ever ; but the microscope betrayed an extraordinary change of configu- 

 ration. Most of the brood had crowded together ; many extended on re- 

 novation of their native element, and pursuing their course, they seemed 

 to be occupied among neighbouring muddy particles, as if in quest of some- 

 thing there. But, at this time, all were clumsy and disfigured ; some irre- 

 gular, some truncate, others almost spherical — some not half the size of 

 symmetrical animals. — Figs. 8, 9. Had it not been for uninterrupted obser- 

 vation, no one could have identified these distorted beings with the original 

 perfect planulse, Plate XXXIV. fig. 7. 



Some of the original brood survived 27 or 28 days, though much con- 

 tracted . Their vivid colour remained unfaded long after the symptoms of 

 animation had ceased. 



I have been unable to discover any essential difference relative to the 

 facts disclosed by the pure white planulae occupying the vesicles of the 

 Scrtularia falcata, and those afforded by the yellow. On the 7th of May, 

 many of the white escaped from vesicles within which no motion had been 

 sensible on the first of that month. They resembled the yellow exactly, 

 only seeming of rather inferior size, Plate XXXIV. fig. 10, enlarged. But 

 while inspecting this figure, it must be noted that the shape of the planul* 

 is liable to perpetual modification ; it is dependent on many circumstances 

 — temperature, time, age, as well as the will of the animal. The form of 

 all, when most perfect, is certainly somewhat conical, with a rounded head, 

 or anterior tapering downwards, and flattened below. Nevertheless, some 

 appear of more linear form, the sides being parallel, and the extremities 

 nearly equal, while in complete vigour. 



It is established that when yellow planulse occupy the vesicles, yel- 

 low spots originate on the vessel, and where the planulte contained are 

 white, the spots following their production are white. The observer, how- 

 ever, is frequently precluded from following this progress ; he finds them 

 without witnessing the appearance or quiescence of the planulse. They 

 originate unobserved. 



