Microscopical Essays, 



4°5 



felves fo firmly by the tail to aquatic plants, flones, Sec. as not to 

 be eafily driven from the place where they have fixed themfelves ; 

 they often further ftrengthen thefe attachments, by means of one 

 or two of their arms, which they throw out and fix to adjacent 

 fubfiances as fo many anchors. 



The mouth of the polype, or hydra, is fituated at the fore-part 

 of the body, in the middle between the (hooting forth of the 

 arms. The mouth affumes different appearances, according to 

 the different purpofes of the infect ; fometimes it is lengthened 

 out, and forms a little conical nipple, as at Fig. 13, Plate 

 XXIII. A; fometimes it appears truncated, as at Fig. 8, Plate 

 XXI ; at other times the interval between the arms appears clofed, 

 as at Fig. 2 and 12, Plate XXIII. A; or hollow, as at Fig. 11, 

 Plate XXIII. A. If it is obferved with a deep magnifier, in 

 either of the two laft cafes, a fmall aperture may be difcovered. 



The mouth of the polype opens into the flomach, which is a 

 kind of bag, or gut, that goes from head to tail; this may be 

 perceived by the naked eye, when they are expofed to a ftrong 

 light, or a candle placed on the oppofite fide to the eye ; for the 

 colour of the polype does not deftroy the tranfparency thereof. 

 The ftomach will, however, be better feen,, if the eye be a {lifted 

 by a deep magnifier ; one of them is reprefented as highly mag- 

 nified, at Fig. 8, Plate XXL To be fully fatisfied whether they 

 were perforated throughout, Mr. Trembley cut one tranlverfely 

 into three parts ; each piece immediately contracled itfelf, and 

 became very fhort, and being placed in a mallow glafs full of water, 

 and viewed through the microfcope, they were found to be vifibly 

 perforated. They are reprefented as they appear in the micro- 



