248 Miscellaneous. 



elements which compose the branchial lamellae, and to establish the 

 identity of the structure of these organs in all the types examined, 

 whether they belong to the type of unipennate branchiae or to that 

 of bipennate branchiae. 



1. The epithelium of the branchia always appears formed of two 

 kinds of elements — of columnar cells inserted upon the basal mem- 

 brane by a slender, sometimes ramified process, and terminated at 

 the other end by a ciliated disk ; the disks of contiguous cells touch 

 one another, so as to form a regular and continuous mosaic, beneath 

 which, between the groups of the preceding cells, occur small 

 spherical or ovoid masses of muciparous cells. The epithelium of 

 the mantle and of the false branchia also presents these two kinds 

 of elements. 



2. The basal membrane of the epithelium forms upon each sur- 

 face, along the inner margin in the unipennate branchiae, a resistant 

 thickening of triangular section, which is the supposed supporting 

 cartilaginous rod. This thickening is formed of superposed layers 

 and presents no trace of cells. It is therefore not cartilage, as has 

 so often been said. 



3. Between the two laminae of the basal membrane there are 

 stellate cells with anastomosing processes, sometimes isolated, some- 

 times collected into groups, especially near the margins, where they 

 are sometimes arranged with regularity. This is the ordinary con- 

 nective tissue of the lacunaa. 



4. A bundle of longitudinal muscular fibres extends quite to the 

 point ; from it are detached fibres which run obliquely towards the 

 outer margin. 



Other fibres, transverse and often distinctly ramified at their 

 extremity, are less constant in their occurrence and arrangement. 

 This is the case also with another system of longitudinal fibres, 

 sometimes forming a close grating with the preceding. All these 

 fibres meet on both sides of the central lacuna. 



The innervation of the branchia compared with that of the false 

 branchia will be the subject of another communication. 



With regard to the circulation, I have been led to resume the 

 recent researches of MM, Wegmann and Boutan. These anatomists 

 have indicated, one of them in Haliotis, the other in Fissurella, the 

 existence of vessels in each margin of the lamella and united by 

 transverse capillaries. Numerous injections, sections, and trans- 

 parent preparations obtained by removing the epithelium by reagents 

 enable me to assert that in these two genera, as in all those which 

 I have hitherto studied, there are neither vessels nor capillaries — 

 that is to say, there is no canal circumscribed by a muscular or 

 endothelial coat. 



According to M. Boutan *, " the lamellae are formed of a spongy 

 tissue filled with little lacunae, the excessively minute size of which 

 must cause them to be assimilated to capillaries." Now any 

 assimilation of lacunae, however smaU they may be, to capillaries, 



* Arch, de Zool. exp6r, s6r, 2, tome iii., Suppl. p. 37. 



