358 Prof. E. Claparéde on the Structure of the Annelida. 
parency of the crystalline is incontestable in many cases, Miiller’s 
opinion as to the functional value of this organ must not be re- 
jected. The eyes of the Nereides and of most of the Annelida 
appear to be destitute of any apparatus of accommodation. If 
therefore we assume that the perceptive elements are lodged be- 
tween the granules of the pigment, only objects placed at a 
determinate and perfectly fixed distance can project their images 
upon the surface of this choroid pigment. The vision of the 
animal would, in this case, necessarily be very restricted. This 
difficulty disappears if we seek in the crystalline at once a re- 
fractive body and a perceptive organ, nearly as we seem compelled 
to admit with regard to the crystalline cones of the Arthropoda. 
The image projected at various depths in the crystalline by 
objects placed at variable distances would then always be formed 
in a sensitive layer. ; 
Regeneration of Mutilated Parts. 
The observations of Bonnet upon the regeneration of muti- 
lated parts in the Earthworms, confirmed by Lyonnet, Réau- 
mur, Dugés, &c., were hesitatingly doubted by Vandelius* 
and Bose +, and more recently and positively by Dr. Williams f, 
M. Vogt §, and others. We must therefore be thankful to 
those who, like Dr. Baird ||, have brought to light certain early 
observations, or, like M. de Quatrefages J, have corroborated 
and confirmed them by fresh experiments. 
The reproduction of mutilated parts in the Annelida is m- 
contestable. A great number of these worms, perhaps all, can | 
even reproduce the anterior region including the head. Among 
* “Dominici Vandelii philosophi ac medici dissertationes tres. De 
Aponi Thermis, de nonnullis insectis terrestribus, et Zoophytis marinis, et de 
Vermium terre reproductione, atque Tenia canis. Padua, 1758,” pp. 98- 
147. This work, which seems to have been forgotten, is nevertheless the 
production of a good observer. In very careful experiments, repeated for 
two successive years, he did not succeed in seeing mutilated EKarthworms 
reproduce their anterior extremity. He, nevertheless, prudently con- 
cludes that these experiments require to be made with extreme care, and 
does not accuse Réaumur of having deceived himself. We know that 
Dugés afterwards likewise began by obtaining negative results, but that 
subsequent experiments succeeded with him completely. The regeneration 
of the anterior part takes place, in fact, only when the number of seg- 
ments removed is not too great. 
+ Histoire Naturelle des Vers, tome i. pp, 128 & 215. 
ae rap Pos on the British Annelides,” Report of the British Association, 
1851, p. 247. 
§ Vaceniane iiber niitzliche und schadliche, verkannte und verlaum- 
dete Thiere. Liepzig, 1864, p. 91. ~ 
|| Johnston’s Catalogue of British non-parasitical Worms. Appendix. 
“{ Ann, Sci. Nat. tome ii. 1844, p. 100; Hist. Nat. des Anneleés, tome i. 
p. 126. : 
