INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 859 



arrives in abundance at the level of tlae mouth of the intermediary 

 trunk, to which it applies the valvule aud which it thus stojis. It is 

 thus obliged to pass entirely into the afferent vessel of tlie branchia, 

 and, consequently, into the branchia, of which the activity is thus 

 greatly increased. When, on the contrary, during sojourn in the air, 

 the collapsed branchia does not act, the blood of the afferent vessel of 

 the branchia, arriving en masse on the edge of the spur, there divides 

 into two currents, one of which penetrates into the in-oper afferent 

 vessel of the lung, and the other into the intermediary trunk, of which 

 it augments the tension, and which distributes a part of it to the floor 

 of the lung, and reconducts the rest to the heart. By this means the 

 activity of the pulmonary circulation is increased during the repose 

 of the branchia. Hence results this interesting fact, that the Ampul- 

 larice, which are Pectinibranchiata in which j)ulmonary respiration 

 has made its appearance, have the respiratory vessels disposed in such 

 a manner that, when this newly-introduced function suspends its 

 activity, all the blood which should have traversed the pulmonary 

 network, is constrained to traverse the branchial system, where its 

 hfematosis is assured. This curious arrangement may suffice to ex- 

 plain the preservation of the branchia in Gasteropoda, in which the 

 lung has attained so remarkable a development, and which might have 

 become pm*ely pulmonary animals. 



The distribution of the vessels in the pulmonary walls merits 

 special mention. They form a double system of portal veins ; that is 

 to say, the vessels form on their journey two successive networks 

 separated by intermediary trunks. This arrangement, a little less 

 accentuated on the floor than on the roof, added to the presence of a 

 fine vibratile epithelium on the course of the pulmonary vessels, proves 

 the active part of this apparatus as an organ of haematosis. 



Doridse of the Northern Seas.* — Dr. E. Bergh has a technical 

 paper on this group ; in his introduction he points out how few are 

 the species — not more than twenty-two — that are known ; he further 

 states that Alder and Hancock, although they have brought into 

 relief a number of anatomical difi'erences, still recognize only three 

 genera, Doris, Lamellidoris, and Acantliodoris. The author considers 

 that there are a larger number of genera, and that these may be 

 divided into two groups— to which he applies the names of Crypto- 

 branchiatfe and Eleutherobranchiatfe, according as the gills are or are 

 not retractile ; the former grouj) appears to be somewhat cosmo- 

 politan and contains the genera Archidoris, Biaulula, Cadlina, 

 Joorunna, Aldisa, and Bostanga ; the latter is confined, so far as we 

 know, to the colder regions, and contains Acantliodoris, Adalaria, 

 Lamellidoris, Goniodoris, and Doridunculus. 



Glands in the Foot of the Lamellibrancliiata. j — M. Justus 

 Carriere gives a short sketch of the very difierent views which have 

 been held as to the characters of the byssus-gland, noting that 

 Eeaumur regarded the byssus as being formed by the glutinous 



* 'Arch, fiir Naturg.,' xlv. (1879) p. 340. 



t ' Arbeit. Zool.-Zoot. Inst. Wiirzburg,' v. (1879) p. 56. 



