SERTULARIA. 155 



quired four. Its progress is shown in figures 5, 6-9, 1 1, somewhat exceeding 

 the natural size, and the three latter figures, 7, 10, 12, enlarged. This 

 same specimen had three cells on May 22, and next day four ; and so it 

 continued until July 25, when delineated ; but decay prevented maturity 

 of the fourth. 



During observations protracted for several weeks on all the nascent 

 Sertularise, fewer and fewer hydrae protruded from their cells, and this 

 chiefly in proportion to the lapse of time from their origin. Several ap- 

 peared on July 18 ; in another week only one, though the cells apparently 

 still contained living inmates. Sometimes these creatures, and indeed 

 the tenants of all Sertularise, persist in long retreat. When induced to 

 issue forth by renovation of the limpid element, they speedily retire to 

 their respective dwellings, after a transient display. 



It is obvious, therefore, that two differently formed vesicles are borne 

 by the Sertularia abietina, a fact also incident to a few other Sertularia;. 

 The precise nature of the pedestal I have been unable to ascertain ; but 

 circumstances infer that it may be possibly an ampuUate or flask-shaped 

 vesicle originally, whereon the other spherule is generated. Specimens 

 have occurred with vesicles resembling the ordinary ampullate vesicle of the 

 Sertularia or Plumularia falcata, and scarcely in less profusion, though of 

 inferior fecundity. About 26 or 27, almost in a double row, with con- 

 tents nearly white, were crowded towards the side of a branch not an inch 

 in length.— Plate XXV. fig. 1. 



Other specimens of the same group bore a compound vesicle, with a 

 pedestal as those above described, the spherule containing a single yellow 

 globular corpusculum, the pedestal vascular as before. — Plate XXV. 

 figs. 2, 3. Planulse of a fine saffron yellow issued from the spherules, 

 about half a line long, the head obtuse, and the tail pointed, but not 

 alike pyriform until beginning to contract, when some resemblance to those 

 already represented ensued. — Fig. 4. 



Here the reader should be apprized that great diversity occurs in the 

 shape of the same planulse, from whatever zoophyte they come. Nothing 

 can be more variable than their soft, extensile, and contractile bodies, in 

 motion or at rest ; and according to the freshness of their element or the 



