Fecundation of the Ovum* 305 



effected, the ovum completes its development iu the manner 

 described by Nelson. 



In the Lumbrici, which were also studied by Meissner, things 

 go on rather differently. In the ninth and tenth segments of 

 their bodies, these animals ])ossess four vesicles, which were 

 formerly regarded as testicles, and the correct interpretation of 

 which was first given by Von Siebold*, who states them to be 

 seminal receptacles, — a function which also appears to be attri- 

 buted to them by Van Benedenf. 



These vesicles open externally by means of two small apertures, 

 formerly mentioned by Leo J. They have no communication 

 of any kind with the ovaries, and it is nevertheless in their in- 

 terior that the mature eggs are found. They probably arrive 

 there from the exterior during copulation, so that in fact these 

 organs should bear the name of common receptacles of the 

 ova and semen, or of sacs of fecundation. The ovarian ova 

 which possess a vitelline membrane and a germinal vesicle have 

 lost these two elements when they arrive in the common recep- 

 tacles, where they consequently swim completely naked. When 

 there, they are assailed by the spermatozoa, which penetrate in 

 crowds into the substance of the vitellus by a corkscrew-like 

 movement. The united movements of the tails of all these 

 spermatozoa at the surface of the ovum produce an appear- 

 ance of waves. The segmentation of the ova commences in the 

 receptacles, and they are afterwards extruded in a common 

 capsule. 



In this memoir Meissner confirms the discoveries of Barry, 

 inasmuch as he also certainly saw spermatozoa in the interior of 

 the ovum of the Rabbit, although he could not positively con- 

 vince himself of the presence of the micropyle. This is a fact 

 of great importance. We may always suppose that there is 

 some error in speaking of the ova of Anodonta and Unios ; we 

 may suppose that the spermatozoa which appear to be within 

 them, may be in reality above or below them. But it is im- 

 possible to suppose that an object seen within the zona pellucida 

 of the Rabbit may be situated above or below it. The object in 

 question in fact is much too large, and it is impossible that the 

 internal and external surfaces of the zona pellucida can be in focus 

 at the same time. The same may be said, with still better 

 reason, of the ova of the Frog, within which, as we have seen, 

 Newport discovered spermatozoa. 



* Lehrbuch der vergleichenden Anatomie. 



t Report on a paper of Van Beneden's on the D^eloppement du Lombric 

 terrestre, in Bull, de TAcad. Roy. de Belgique, xx. 



X De Structura Lumbrici terrestris. Regiomonli, 1820. 

 Ann. ^ Mag. N. Hist. Ser. 2. Vol xvii. 20 



