320 E. RAT LANKEStER. 



Remarks on the Shell-gland of Cyclas and the Planula 

 of Ltmn^us. By E. Ray Lankester, M.A., F.R.S. 

 With Plate XXIV. 



Controversy is one of the most wasteful ways in which 

 a man can employ himself with pen and paper. I do not 

 propose, therefore^ to enter into a verbal dispute with the 

 zoologists who have recently expressed opinions at variance 

 with the results which I have published relative to the de- 

 velopmental phenomena of Mollusca; but I am anxious to 

 take an opportunity of briefly reasserting the cliief features 

 of those results ; since in late publications, partly by deli- 

 berate misrepresentation (Fol), and partly by ignorance 

 (Jherings), they have been made to appear different in point 

 of date, and of actual significance from what they really are. 



My observations, commenced in 1871, (Pisidium, Limax, 

 and Limnseus, 1871 ; Aplysia, Pleurobranchidium, Polycera, 

 Tergipes, Sepia, Loligo, 1871-72; Neritina, 1873; Loligo* 

 (bis), Limnseus (bis), Paludina, 1874) led me to certain 

 results of a general character besides those which had refer- 

 ence to this or that species only, and the most important of 

 these were briefly indicated in a paper in the ' Annals of 

 Natural History,' February, 1873. I briefly described, in 

 that paper, the shell-gland of Aplysia and of Pisidium, and 

 introduced the term '^ shell-gland,^^ which has since been 

 adopted by German writers as " Schalendriise." I also de- 

 scribed, for the first time, the formation of an invaginate 

 Gastrula, with closure of the orifice of invagination in several 

 Nudibranchs and in Pisidium ; thus extending Kowalew- 

 sky's observation to the Mollusca, he having previously 

 mentioned the invaginate Gastrula as occurring in the de- 

 velopment of the Heteropod Atlanta. This publication 

 was anterior by some months to that of Professor Ganin, of 

 Warsaw, who in 1873 gave an account of the development of 

 Cyclas and of Limnaeus, difiering very greatly from my 

 own. 



In the first month of 1874, before I left England for a 

 second sojourn at Naples, the MS. and figures forming the 

 memoir published in 1875 were deposited with the Royal 

 Society. On returning to England in July, 1874, 1 resumed 

 the study of the development of Liniiiajus, and published in 

 this Journal, October, 1874, a paper which gave an outline 

 of the results embodied in my larger memoir ('Phil. Trans.,' 

 1875), besides the results obtained from Limnaeus. 



