360 APPENDIX. 



threads, and of shorter ones furnished with a sucker.- 

 As a longer tliread of a blueish colour always hung 

 (in the Physalia glaucd) close to the shorter one, I 

 imagine that these two threads represented an un- 

 formed young one, hanging to the mother, and 

 that the longer thread was the first arm for seizing 

 prey, the shorter one a stomach ; it is not neces- 

 sary for the bladder to get filled with air, as the 

 young one is carried by the mother. 



Wishing to see whether the small cavity at the 

 back process of the Physalia glauca was really an 

 opening closed by a muscular valve, I took the 

 bladder in the middle, pressed the air towards the 

 end of the back process, and saw how a small 

 round opening was formed in the place of the 

 cavity out of which the air pressed. When I left 

 off pressing, the opening closed again ; the bladder 

 became quite slack by the air being pressed out. 



II. VELELLJE. 



The flat body of the velellae, swimming on the 

 surface of the water, has the appearance of a paral- 

 lelogram with rounded corners ; its exterior skin 

 is very soft, and incloses two transparent gristles, 

 joined together in the middle, and forming, an 

 ellipse, with concentric stripes. These are a little 

 convex, and lie in the body in a diagonal line. On 

 them stands a transparent gristly semicircular sail, 

 also in a diagonal direction, and in such a manner, 

 that its ends are turned to the exterior edge of the 



