Miscellaneous. 151 



Thus, in sections of the adult O. sexoculata, I have observed in its 

 place a strongly pigmented depression of the integument. 



The constitution of the dorsal organ of G. bioculata, which in 

 reality is only a plate of chitine buried in a depression of the skin, 

 leads to the rejection of the denominations " dorsal gland " (Mo- 

 quin-Taudon), " yellowish-brown spot " (Budge), and " red spot " 

 (Robin), which have been applied to this formation by the authors 

 who have examined it. It seems preferable to designate it by the 

 name of the dorsal chitinous plate. 



2. Male apparatus of Gr. sexoculata.-— The data which we 

 possess as to the male apparatus of G. sexoculata did not enable us to 

 bring this apparatus into the very homogeneous series of the other 

 species of the genus. The most recent memoir on the subject (Robin, 

 1862) still shows it as formed on each side of a simple tube, bent 

 into a U» terminating on the one hand in a free point in the an- 

 terior region of the body, and on the other at the male genital 

 aperture, after having been dilated into a sac for the spermato- 

 phores. Yery numerous fine dissections have enabled me to ascer- 

 tain that the outer branch of the U"^!^^'?®'! tube, instead of 

 terminating in a free point, becomes bent back and attenuated, runs 

 backward parallel to the axis of the body, and receives on its outer 

 side the short deferent ducts of the ten testes of the corresponding 

 side. This description enables us to bring the male apparatus of 

 G. sexoculata into the series of forms already described by F. 

 Miiller, Budge, &c. 



3. Skin and Respiration in the Rliyncliohdellea. — Hitherto it has 

 been assumed that the respiration of the Hirudinea is cutaneous, 

 without investigating what differentiations this function might 

 induce in the integument which is its seat. Branchellion alone had 

 attracted some attention. I have examined whether there are not, 

 in the series of the Rhynchobdellea, some particular arrangements 

 which would enable us to explain the origin of the branchiae in the 

 parasite of the Torpedo, and I have ascertained that, in the different 

 genera, the integument presents curious adaptive modifications. The 

 most interesting type in this respect is Pontobdella. In this genus, 

 which is cylindrical (an isolated fact among the Hirudinea), the 

 dermis is swelled into voluminous tubercles. The structure of 

 these formations not having hitherto been noticed, it will be useful 

 to indicate it here, especially as their anatomy exactly accounts for 

 their physiology. 



The tubercle is a dermal projection (not, as M. de Saint-Loup will 

 have it, a mass of epithelial lamellae) covered with epidermis and 

 furnished with muscles of two kinds — retractors, parallel to the axis 

 of the tubercle, and extensors, which are radial. Capillaries are 

 abundant in them. The extent of the surface, the abundance of its 

 vascularization, and the peculiar development of its musculature 

 place this organ under conditions exceptionally favourable for hsema- 

 tosis, and render the tubercle a respiratory organ, already highly 

 differentiated. 



