NATURE'S CALENDAR 



179 



adults, and in the case of the naked mol- 

 lusks {Niidibranchia) the larvae are fur- 

 nished with a beautiful little glossy spiral 

 shell, which they afterwards lose. The 

 pteropods swim free in all stages. . . . 



" The bivalve shells mostly produce 

 minute young, or larvae, which are at 

 first provided with vibrating cilia, and 

 swim free for several days, as is well 

 known to be the case with the oysters, 

 clams, mussels, tereds, etc. . . . The com- 

 mon fixed ascidians, both simple and 

 compound, mostly produce eggs that 

 hatch into tadpole-shaped young, that 

 swim about for a short time by the un- 

 dulating motions of the tail, but finally 

 become fixed by the head end, and losing, 

 or rather absorbing, the tail portion, rap- 

 idly develop into the ordinary forms of 

 the ascidians." 



To this list must be added great num- 

 bers of swimming larvae of starfishes, sea- 

 eggs, and other echinoderms, including 

 various holothurians. 



The jellytishes, young and old, now 

 throng the surface waters, and illuminate 

 them with that beautiful phosphoresence 

 of which these and the colonies of wan- 

 dering hydroids and ascidians, such as 

 the exquisite salpa chains, are mainly the 

 authors. Sometimes in August that mar- 

 vellously beautiful creature, the Portu- 

 guese man-of-war, comes sailing into our 

 harbors from the tropics, its iridescent 

 sail hoisted to catch the gentle wind. 



August 8 



August 9 



