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II. " Researches on the Poison-apparatus in the Actiniadce." 

 By PHILIP HENRY GOSSE, Esq., F.R.S. Received January 

 18, 1858. 



(Abstract.) 



The organs which have been termed " thread-cells,'* *' thread- 

 capsules," "urticating organs," "lasso-cells," &c., I propose to call 

 cnidce. They are found in various tissues of the body, but are 

 specially localized in two sets of organs, which I call craspeda and 

 acontia. The craspeda are gelatinous cords connected throughout 

 their length with the free edges of the muscular septa. The acontia 

 are somewhat similar cords, but free throughout, except at their 

 base, where they are inserted into the septa. The cord-like appear- 

 ance of these latter organs is, however, illusory, as each is a narrow 

 ribbon with involute margins. Both the craspeda and the acontia 

 are composed of a clear plasma, in which many cnidce are crowded. 



The craspeda appear to be universally possessed by this tribe of 

 animals, but the acontia are limited to a few genera, principally 

 Sagartia and Adamsia. They are ejected from the body of the 

 animal, and are again withdrawn. 



For the emission of these organs special orifices exist, which I 

 term cinclides. These are minute perforations of the muscular 

 coats and the integument, bearing a resemblance in appearance to 

 the spiracles of insects. Being placed in the interseptal spaces, they 

 have a perpendicular arrangement, but are not regularly disposed in 

 any other respect. They can be opened widely, or perfectly closed 

 at the will of the animal ; and are well seen, under a low power of 

 the microscope, when a Sagartia bellis or dianthus is much dis- 

 tended in a parallel-sided glass vessel, with a strong light behind it. 

 The width of these orifices varies from -^^ th to -g^th of an inch. 

 No ciliary current passes through them. 



Under irritation the Sagartia forcibly and repeatedly contracts its 

 body, forcing out the water which had distended its aquiferous canals 

 and the general cavity of the body. Much of the fluid finds vent at 

 these foramina, carrying with it the free floating part of some or 

 other of the numerous acontia, each through that cinclis which 

 happens to lie nearest to it. The frequency with which the acontia 



