308 M. E. Claparede on the Theory of the 



The numerous facts to which we have drawn attention prove 

 more than sufficiently that fecundation is eflfected by an actual 

 penetration of the spermatozoa into the interior of the ova, and 

 that very often, if not always, this penetration takes place 

 through a micropyle. It remains to be seen in what envelope 

 of the ovum this exists, and if it is always possible to explain its 

 formation in the manner of Loven* and Leuckart, or in that of 

 Meissner. Johannes Miiller has, not long since t, indicated a 

 peculiar structure in the external membrane of the ova of certain 

 fishes, especially our river fish, — a structure which has also been 

 investigated by Lereboullet J. This membrane is pierced by a 

 multitude of little canals, passing from one surface to the other, 

 and dilating into a funnel-like form at each surface, so that the 

 membrane presents a facetted appearance. This structure is 

 particularly remarkable in the Perch {Perca fluviatilis), the egg 

 of which has a very thick external membrane ; but it is equally 

 striking from its elegant appearance in the Ruffe [Acerina 

 cernua) and the Sticklebacks {Gasterosteus trachurus, lagurus, 

 pungiiius, &c.). This structure appears to have been previously 

 seen by Vogt§, who describes a shagreened appearance of the 

 cortical membrane in the Coregonus palea ; but he seems not to 

 have remarked that this appearance was due to the presence of 

 a multitude of little canals, of which the number, according to 

 J. Miiller, amounts to more than 1,1000 in the egg of the 

 Perch. It is in this membrane that the micropyle is situated ||. 

 It is remarkable that this membrane presents a great analogy in 

 structure with that in which the micropyle is placed in the Holo- 

 thuria. This latter is characterized by a sort of striation, — an 

 appearance which is due, according to the opinion of J. Miiller, 

 to a multitude of little prisms placed perpendicularly upon the 

 membrane. It is the membrane that Miiller regards as the 

 cortical membrane [Schalenhaut)^, and Leuckart as the vitelline 

 membrane**. 



* Bidrag till kannedomeu om utvecklingeii af MoUusca acephala. 

 Stockholm, 1848. 



t Ueber zahlreiche Porenkanale in der Eikapsel der Fische. Monatsber. 

 der Berl. Akad., March 1854. 



X Ann. des Sci. Nat. 1854. 



§ Embryologie des Salmones, in Agassiz, Hist. nat. des Poissons d'eau 

 douce de I'Europe centrale. 1842. 



II This micropyle, or at least the funnel at the bottom of which it opens, 

 is sometimes so large, that Bruch has found it with the naked eye in the 

 egg of the Trout {Fario lacustris) and the Salmon {Salmo salar). Zeitschr. 

 fiir wiss. Zoologie, May 1855. The funnel itself was already known to 

 Von Baer in Cyprinus blicca, — ^Entwickelungsgeschichte der Fische. 

 Leipzig, 1835. 



51 Ueber die Larven und die Metamorphose der Holothurien und Asterien. 

 1860. ** Zusatz zu Bischoff' s Widerlegung, &c. 



