ANATOMY OF THE TEREBRATULA. 21 



received into the intervisceral, 9, intermuscular and pallial, 5, 6, sinuses, which will 

 perform the double but closely allied functions of veins and absorbents. 



The streams of sea-water excited and maintained by the complex ciliated structure of 

 the mantle, will effect the requisite respiratory changes as they course over the delicately 

 coated, branched, sinuses of the pallial lobes ; these, therefore, form the chief seat of the 

 breathing function ; but, wherever similar currents come in contact with the vascular 

 system, to that extent the respiratory operations will be diffused. 



GENERATIVE SYSTEM. 



The generative organs have presented the same form in all the individuals of the 

 different species of Terebratula examined by me. This form corresponds with that of the 

 pallial sinuses in which they seem to be situated. The figures 15 and 16 r, r, pi. 22, 

 ' Zool. Trans, vol. I,' from the Terebratula Sowerbii, represent so closely the general form 

 and disposition of the same organs in Terebratula Jlavescens, that it seems needless to 

 repeat the figures of them in the latter species. 



I have observed, however, a manifest difference of texture and colour in the gene- 

 rative organs of different individuals of Ter. Jlavescens collected at the same period in the 

 neighbourhood of Port Jackson, by my friend Mr. George Bennett, E.L.S., and transmitted 

 in the same preserving liquid. In some specimens the organs are better defined, more 

 compact, and of a paler colour : in others the organs are broader or more diffused, and of 

 a deeper yellow colour. 



On a microscopic examination of the first kind, they are found to consist of an 

 aggregate of minute cells, closely resembUng those in the half mature testes of the common 

 oyster. I conclude, therefore, that they are the male generative organ in the Terebratula, 

 and that the individuals of this genus are dioecious, not, as I formerly supposed, simple 

 hermaphrodites. The true ova are very plainly manifested in the broader and deeper- 

 coloured dendritic organs. They are developed, like the sperm-cells, between the outer 

 layer of the mantle and the delicate tunic of the venous sinus, and protrude into that 

 cavity, pushing its lining membrane inwards. The generative organs, in the male, as in 

 the female, developed in the ventral lobe of the mantle, commence — if we may term the 

 part next the hinge of the shell their beginning — by a loop, pi. 3, fig. 1, 12, on each side of 

 that lobe, situated at the point of bifurcation of the two sinuses ; these loops are shown in 

 fig. 1, pi. 3, the inner layer of the mantle with the adherent tunic of the sinus being reflected 

 to show the looped portions of the ovaria, 12, 12. lu the dorsal lobe the generative organ 

 commences at about the same distance from the hinge, by a simple obtuse extremity ; and 

 follows, as it advances, the ramifications of the sinus in which it is lodged. There are thus 

 four distinct ovaria or testes ; two in each mantle lobe ; those of the ventral lobe being 

 doubled, or bent upon themselves, near the cardinal attached border of the lobe. It may 

 be presumed that the embryos developed under the influence of their suspension in the 



