CONCHIFERS. 713 
ego". 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 
egos arrive at the lobes of the mantle, and cover the blood-vessels 
that are distributed there*. In the Lamellibranchiata Prevost 
discovered in 1823 distinct sexes in Unio®. 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 
Epwarps, and others, and especially by very exact investigations 
of C. T. Von Stepoip*, In the mean time, this interesting pecu- 
larity 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®, The spermatozoa have a long thin tail and a conspicuously 
distinct body, like a knob, which is very small and elongated. 
The ¢estes 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 Physiologie, 11. 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. 1. pp. 152—156, Pl. 22, 
fig. 11¢ 167, Pl. 23, fig. r1w, fig. 15m; in these figures the eggs are represented 
partly in the mantle ; there are eggs also lying on the mantle, which O. F. Muriier 
described and figured as ovarium ramosum in Orbicula, Zool. Danic. Tab. 4, fig. 7. 
[See, however, OweEn’s further description of the generative organs in Terebratula, in 
his Jntroduction cited above, p. 710 and Plate mt. fig. 1. He concludes that Ter, 
Jflavescens is diceceous. | 
3 De la génération de la moule des peintres, Mém. de la Soc. de Physique et d’ Hist. 
Nat, de Genéve, 11. 1, pp. 121 and foll. 
4 See these observations, illustrated by figures, in MUELLER’s Archiv, 1837, 
s. 381—392. 
® A. Van LEEUWENHOECK Vijfde vervolg der Brieven, Delft, 1696, 4to, 95 vte Mis- 
sive, blz. 136—155 ; see especially blz. 145. 
