CONCHIFERS. 713 



egg 1 . We have already seen above in the case of the sea-nettles 

 and echinoderms, that the sexual glands (ovaria, testes) might agree 

 entirely in position and external form, so that, without microscopic 

 investigation of their contents, it could not be determined whether 

 they were feminine or masculine, whether they served to prepare 

 the germ or to impregnate it. In the Brachiopoda the ovary alone 

 is known hitherto, which lies behind the liver ; from the ovary the 

 eggs arrive at the lobes of the mantle, and cover the blood-vessels 

 that are distributed there 2 . In the Lamellibranchiata PREVOST 

 discovered in 1823 distinct sexes in Unto 3 . In the male sex, in 

 place of the ovary, a similarly formed part is found, filled with 

 white fluid, which swarms with seminal animalcules. PREVOST 

 saw neither from these nor from those that had ovaries any young 

 ones proceed when he kept them apart, but did when two were 

 placed in contiguity. These observations were confirmed some 

 years afterwards by others of the same kind, of WAGNER, MILNE 

 EDWARDS, and others, and especially by very exact investigations 

 of C. T. VON SiEBOLD 4 . In the mean time, this interesting pecu- 

 liarity is no new discovery of the last years ; and the observations 

 which have been alluded to tend to the confirmation rather of what 

 had already been observed by LEEUWENHOECK a century and a half 

 earlier 6 . The spermatozoa have a long thin tail and a conspicuously 

 distinct body, like a knob, which is very small and elongated. 

 The testes in the male individuals are situated at the same part as 

 the ovaries in the females ; they open at the same place, and appear 

 in the arrangement of their blind tubes to agree with the ovaries. 

 Now that it has been admitted that difference of sex exists in the 



1 MUELLER'S Physiologic, n. p. 618. 



2 CUVIER could not trace the organs of propagation in Lingula; OWEN describes 

 them very briefly in Terebratula and Orbicula, Trans. Zool. Soc. I. pp. 152 156, PI. 11, 

 fig. i if, i6r, PL 23, fig. n w, fig. i5m; in these figures the eggs are represented 

 partly in the mantle ; there are eggs also lying on the mantle, which O. F. MUELLER 

 described and figured as ovarium ramosum in Orbicula, Zool. Danic. Tab. 4, fig. 7. 

 [See, however, OWEN'S further description of the generative organs in Terebratula, in 

 his Introduction cited above, p. 710 and Plate III. fig. i. He concludes that Ter. 

 flavescens is diosceous.] 



3 De la generation de la moule des peinlres, M&m. de la Soc. de Physique et d'ffist. 

 Nat. de Geneve, in. i, pp. 121 and foil. 



4 See these observations, illustrated by figures, in MUELLER'S Archiv, 1837, 



s. 381 39 2 - 



5 A. VAN LEEUWENHOECK Vijfde vervolg der Brieven, Delft, 1696, 4to, 95vte Mis- 

 sive, biz. 136155 ; see especially biz. 145. 



