4:20 



EVENINGS AT THE MICKOSCOPE, 



becomes from some cause arrested, and the contents 

 of the cell remain permanently fixed in a transition 

 state. Thus, a long continued course of patient ob- 

 servation is pretty sure to j^resent some fortuitous 

 combinations, and abnormal conditions, "which greatly 

 elucidate phenomena, that normally seemed to dety 



mvestigation. 



CN'IDA OF B. CRASSI 



coExis, discharged. 



" In "watching any particular cnida, 

 the moment of its emission may be pre- 

 dicted "with tolerable accuracy, by the 

 protrusion of a nipple-shaped wart from 

 the anterior extremity. This is the 

 base of the thread. The process of 

 its protrusion is often slow and gradual, 

 until it has attained a len2;th about 

 equal to twice its own diameter, when 

 it suddenly yields, and the contents of 

 the cnida dart forth. At this instant 

 I have, in many instances, heard a dis- 

 tinct crack or crepitation, both in the 

 examination of this species and of Sa- 

 gartia parasitica. 



" When fully expelled, the thread 

 or wire, which is distinguished by the 

 term edJiorceum^ is often twenty, thirty, 

 or even forty times the length of the 

 cnida; though in some species, as in 

 most of the Sagartice^ it frequently will 

 not exceed one-and-a-half, or two times 

 - the leno-tli of the cnida. 



" The ecthora^a which are discharged 

 by chambered cnidce, are invariably furnished with a 

 peculiar armature. The basal portion, for a length 



