APPENDIX. 311 



Encyclop. Nat. Phen. p. 37*. — Observations which I made many 

 years ago rather confirm the opinion of Dr. J. Rawlins Johnson, that 

 the movements of the leeches are not to be relied upon as indications 

 of any weather : viz. no given motion of theirs is connected neces- 

 saril}^ with any given change which the day is about to sufferf . 



The generation of leeches was, until recently (1822), involved in 

 obscurity and doubt. There was much discussion as to whether 

 they were oviparous or viviparous, and observations in support of 

 each view were published, without settling the question, although 

 certainly the evidence was rather most favourable to those who asserted 

 that the young were brought forth alive. The subject is now well 

 understood. In due season the parturient leech produces its ova 

 with a glairy fluid in which they are evolved. This becomes the 

 nucleus of a cocoon of a sponge-like fibrous texture, and which bears 

 "no unapt resemblance to the cocoon of the silk-worm." It is, 

 however, less in size, of an oval shape, about the size of a filbert, and 

 so light and spongy that it may easily be mistaken for a small 

 sponge. The inner wall of the cocoon is more compact than the 

 external surface ; and the cocoon, as already mentioned, is filled with 

 the glairy fluid, containing from about six to twenty ova. It is 

 buried by the leech in the mud or clay of its pond ; and there the 

 ova are matured and the young born. These escape from their 

 cocoon by a small aperture at one pole ; for, at this period, there is 

 a hole at one or other extremity of the cocoon, or both extremities, 

 prepared for their exit by a prescience which foresaw the need. 



The young, when hatched, are little thicker than packthread, and 

 they grow so slowly that they do not acquire the adult size until they 

 are three years old. They are then fit to be used in medicine. It 

 is said, however, that they do not become fruitful till they are six or 

 seven years old. 



Leeches are extensively used in medicine, and have been so from 

 an early period — so much so, that the doctor is often styled a leech 

 by authors who wrote about Queen Elizabeth's time:|:, and since, — 

 no doubt the synonym being intended to indicate their healing power, 

 and not any wish on the doctor's part to draw the golden fee — the 

 heart' s-blood only of the usurious. Ancient authors treat also co- 

 piously of the accidents and dangers that flow from the swallowing 

 of leeches, and from their getting into the mouth and throat ; and 



* " On dit cependant, que dans certaines parties de la France, et entre autres 

 aux environs de Bourbonne-les-bains,leshabitans de la campagne n'ont pas d'autres 

 barometres qu'une carafFe d'eau, contenant quelques sangsues avec un peu de terre 

 au fond, et meme une echelle en bois graduee, pour juger par le degre d'eievation 

 ou d'abaissement des sangsues, celui du beau ou du niauvais temps." — Blainville, 

 who, however, is sceptical on the point, and questions the fact. Garner says it is 

 tlie horse-leech which, " kept in a bottle, forms so good a barometer, foretelling 

 bad weather by its restlessness." — Stafford, p. 331. See Moq.-Tand. p. 213. 

 t Watson also denies their barometrical virtue. — Disp. p. 14. 

 X " Wise Leeches will not vain receipts obtrude, 



While growing pains pronounce the humours crude ; 



Deaf to complaints, they wait upon the ill 



Till some soft crisis authori/.c their skill." — Dryden. 



