314 



Z. ASCIDIOIDA. 



Alcyonella. 



ovary. If a recently dead specimen in which the papillae are reduced 

 to the state above described, be examined with the lens, a succession 

 of air-bubbles are seen frequently escaping from the horny tubes. 

 By the successive formation and ascent of these bubbles, the ova 

 which at this period are loose and floating in the tubes, are gradually 

 elevated and conveyed to the exterior. In November, many of the 

 specimens were seen with air-bubbles and ova successively escaping, 

 and the external surface was covei'ed by ova thus conveyed to the ex- 

 terior. Those specimens which were black and putrid, and appeared 

 to have been dead some time, exhibited the horny tubes nearly de- 

 void of ova. After a time the horny basis itself becomes softened, 

 and appears to undergo decomposition. During the following spring, 

 according to the evidence of Vaucher and Raspail, the horny envelope 

 of each ovum separates into two lateral halves adhering on one side 

 as by a hinge. From these valves a small gelatinous tubercle pro- 

 jects, which soon expands into a distinct polype, and gradually be- 

 comes elongated into a tubular form. From the sides of this tubu- 

 lar polype, small gelatinous buds soon appear, and these again be- 

 come developed into distinct polypes ; the tubular parietes gradually 

 become consolidated, and form the horny basis of the mature Al- 

 cyonella." 



Fig. 48. 



Si 



^ 



