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APPENDIX, 



contains and protects the ova, on submerged stones and plants. This 

 capsule was first described by Linnaeus under the name of Coccus 

 aquaticus {Faun. Suec. p. 220). Bergmann first ascertained its 

 real nature ; and Linnaeus, much to his own surprise, confirmed the 

 truth of Bergmann's discovery by personal observation. The capsule 

 was viewed, however, as an egg of an anomalous character*, and the 

 correcter view grew up with a more correct or precise j)hysiology. 

 The leech deposits it throughout the summer months, each individual 

 doing so several times ; and Dr. J. II. Johnson refined too much, 

 and was wrong, when he limited the deposition of the ova to two 

 periods of the year, — the months of J uly and October. The capsule 

 contains from six to twelve ova imbedded in a gelatinous mass. 

 These ova go through the various stages, and the young — like to the 

 parent except in colour — escape from the capsule in from 30 to 70 

 days from its deposition, the peiiod being regulated, principally, by 

 the temperature of the water. 



Dr. J. R. Johnson gives the following account of the production 

 of the ova and capsule : — The leech attaches itself by the posterior 

 sucker, and becomes constricted both above and below the clitellus. 

 In a short time this part becomes of a milky-white colour from the 

 formation of a film or membrane, into which the animal forces, with 

 some effort, the whole contents of the uterus. This done, the indi- 

 vidual elongates the anterior portion of the body, and thus loosening 

 the enveloping membrane, withdraws its head from it, as from a 

 collar. " In some instances, when this membrane cannot be readily 

 detached, I have observed the animal to bend back its head, and 

 then taking it in its mouth, and drawing it gently, is thus enabled to 

 remove it. From the first formation of this membrane or capsule, 

 to its removal from the body, twenty minutes usually elapse. It is, 

 at this time, very elastic, and of no determinate figure. After the 

 Ilirudo vulgaris has firmly fixed it to some surrounding substance, it 

 fashions it with its mouth, until it presents an oval form." — *' It 

 afterwards returns once or twice to survey it, when all farther notice 

 of it ceases.*' — The capsules are at first greyish-white, but in ten or 

 fifteen minutes change to an amber colour. They differ much as to 

 size, but are usually about three lines in length and two in breadth, 

 convex above and flattened beneath. The dark points mark the 

 openings left in the capsule by the manner in which the leech deposits 

 it, and are those places from which (the resistance there being less 

 than in any other part) the young escape. Previous to their birth 

 ** it is not a little amusing to witness their exertions to escape from 

 their imprisonment. They contract themselves, as it respects their 

 length, into as small a compass as possible, and then forcibly push 

 forward the head, butting, as it were, at the dark point of the cap- 

 sule, to effect their escape. After many efforts, they succeed in 



* " In the animal kingdom there has indeed been discovered a leech {Hirudo 

 octoculata), which produces one egg, and from this proceed eight, ten or more 

 young. But it may be questioned whether this is really a single e^^^ or whether 

 it is not several connected together by some mucilaginous matter. In plants there 

 is no instance of this known to me." — TVilldenow. 



