Miscellaneous. 195 



collected still living among the carcasses of P. virgo which strewed 

 the banks of the Garonne, we have not observed a single one the 

 ovaries of which were not almost completely empty. On opening 

 the abdomen after oviposition, we have only found a double sac of 

 considerable capacity, formed by a membrane of extreme delicacy, 

 receiving at its interior part a great number of ovigerous sheaths of 

 three or four chambers containing an equal number of ova in course 

 of formation. Other ova, more advanced in their development, and 

 already furnished with the sort of hood or cap which covers the ex- 

 tremity opposite to that where the head of the embryo will be, are 

 accumulated in greater or less numbers in the great sac into which 

 the ovigerous sheaths open *. 



Is there a special oviduct for each of these two sacs? Leon 

 Dufour says that the sac which constitutes the ovary terminates 

 posteriorly by a tubular neck, which unites with its congener to form 

 a very short oviduct. Swammerdam says nothing of any such ar- 

 rangement ; nor have we ever seen any thing of the kind ; so that we 

 are more disposed to think that there are two oviducts as there are 

 two penises, and that these two oviducts open separately, in the 

 membrane which unites the seventh abdominal segment to the 

 eighth. — Comptes Eendus, October 30, 1876, p. 809. 



On the Nervous System and Muscles of the Echinida. 

 By M. L. Fredericq. 



1. Nervous System. — Notwithstanding the labours of Tiedemann, 

 Van Beneden, Krohn, J. Mliller, Valentin, Baudelot, C. K. Hoff- 

 mann, and Loven, the nervous system of the sea-urchins still presents 

 many obscure points. The investigations that I made this summer 

 at lloscoff on the nervous system of Echinus sphcera and Toxo- 

 pneustes lividus have furnished the following results. 



Anatomy. — The pentagonal nervous ring that surrounds the oeso- 

 phagus, and the five ambulacral cordsl that start from it, are con- 

 tinued within a system of canals which has hitherto been unobserved. 

 This anatomical peculiaritj^ is easily verified, even without the aid 

 of sections, on the cords which run along the ambulacral zones in 

 the interior of the test. Here we find two greatly flattened super- 

 posed canals : the inner one is the ambulacral canal ; the outer one, 

 which is intimately united with the other, contains the ambulacral 

 nerve in the form of a dark- coloured flattened ribbon. The 

 nervous cord floats freely in this sheath, and is only kept in its 

 place by the series of nervous branches which it emits on each side 

 towards the base of the ambulacral vesicles. The envelope of the 

 nervous system is firmly united, but only on the middle Une, with 



* Swammerdam remarked the extreme smallness of the eggs of the 

 Ephemerae : he says, " Oviila cseterum stupendse sunt parvitatis, et vix 

 animadverti queunt." It is, in fact, by this minuteness, that he explains 

 the necessity of the long sojom-n (trienni spatto) that the larvae issuing 

 from the eggs have to make in the water before changing into perfect 

 insects (see 'Biblia Naturae,' torn. ii. p. 255). 



