776 SUMMARY OF CURRENT RESEARCHES RELATING TO 



then presorved in - 2 per cent, chromic acid for twenty-four hours, 

 then passed through serial alcohols to 70 per cent., and kept per- 

 manently in good condition for surface observation. The gill first 

 appears as a nearly median series of folds of ectoderm on the dorsal 

 surface of the vcligcr larva, quite uncovered by the mantle;, which 

 gradually grows over them later on. These gill-folds gradually get 

 drawn into a depression, become plate-like, and get carried downwards 

 and covered by the down-growing mantle; so that the gill now occupies 

 the usual position as a series of plates attached to the inner surface of 

 the mantles hanging into the subpallial chamber. The heart, developed 

 as a space in the mesoderm, is at first in front of the branchial folds, 

 but, as theso are carried forwards, comes to occupy the position found 

 in the adult, behind the gill. In the adult the structure of the gill is 

 the same as that found in Fulgur — consisting of a series of triangular 

 plates, abutting on the leftside on a ridge, which however in this form 

 carries no definite blood-vessel. The osphradium is at the side of the 

 gill, in the usual position. The peculiarity in the development of the 

 gill of Fasciolaria lies in the fact that it appears before the mantle, 

 whereas in Fuhjur, Crepidula, &c, the gill arises on the inner side of 

 tho mantle ; and yet both Fulgur and Fasciolaria develope alike in 

 the egg-capsule. The author regards the mode of development found 

 in Fulgur, &c, as derived and abbreviated from that seen in 

 Fasciolaria ; there is nothing to lead us to consider that the develop- 

 ment in the latter is secondary, but, on the contrary, that all cteno- 

 bianchiates are derived from ancestors like the young Fasciolaria. 

 Considered solely from the point of view of the gill, the phylogenetic 

 development of this structure is repeated ontogenetically in Fascio- 

 laria. 



Referring to Lankester's "schematic mollusc," and to the 

 structure of tho "ctenidium," and to Spengel's theory that the 

 ctonobranch found in most Gastropods was preceded by a ctenidium, 

 of which one series of filaments has been fused with the mantle and 

 lost, the author considers that in the ctenobranch the condition of a 

 ctenidium has never been reached ; that Sigaretus leads on to such a 

 condition, which seems to have been arrived at in Valvata. Taking, 

 therefore, the gill as a basis of classification, he would divide up tho 

 Mollusca into a series which would place those forms with complete 

 ctenidia in the highest place, the simplest condition being found 

 in the larva of Fasciolaria ; but at the same time the author would 

 not place the ctenobranchiates at the bottom of the prosobranchiates, 

 and the zygobranchiates above them as derived from them, for 

 enough is not at present known of the development of Gastropods with 

 a ctenidium. 



Nudibranchs of ' Willem Barents ' Expedition.* — Dr. R. Bergh 

 reports on the seven Arctic genus of Nudibranchs collected by tho 

 ' Willem Barents ' ; anatomical notes are appended to the systematic 

 account of the species. Ghlamylla is a new species, apparently allied 

 to the Coryphellidae, but the caudal portion is short, the dorsal region 



* Bijdrageu tot de Dierkunde, xiii. (1886) 37 pp. (3 pis.). 



