368 ALFRED C. HADDON. 



can be no doubt that these cilia, which, owing to the difficulties 

 of observation, have escaped previous investigators, are homolo- 

 gous with the cilia or ciliated tuft found in a similar spot of the 

 pre-oral lobe in some Lamellibranchiata,^ Dentalium," Chiton,^ 

 Heteropoda* and Pteropoda,^ and which is of such constant 

 occurrence amongst the Vermes. These cilia are retained till 

 the velum itself is lost. I have observed them in Fiona, Poly- 

 eera quadrilineata, Elysia, and Philine aperta, and have no 

 doubt that they are characteristic of the whole group. 



The character of the groove at the edge of the velum and its 

 relation to the mouth is well shown in figs. 4 and 5. The groove 

 is clothed with fine cilia and the lower border has a fringe of 

 larger cilia, but these are not nearly so large as the powerful 

 motor cilia of the upper border. We thus have a pre- and a 

 post-oral circle of cilia. This groove has been described and 

 figured by Fol as occurring in Pteropods and Heteropods, and is 

 indicated by Lankester in a sketch of the veliger of Polycera 

 quadrilineata, though not described by him.^ Fol ascribes a 

 nutritive function to this groove. Though I carefully looked for 

 food particles passing along it, I was disappointed, but I have 

 no doubt that such is the case. Balfour further alludes to it in 

 vol. ii, p. 306, of his ' Treatise.' The velar groove is probably 

 common to all the Nudibranchs. 



In all the Gasteropoda I have examined I have found a patch 

 of cilia either round the anus, or at that spot where the anus 

 will appear. 



I have often seen, in optical section, thickenings of the epi- 

 blast in the regions of the supra-oesophageal and pedal ganglia, 

 and have no doubt that they were the rudiments of the nervous 

 system, but this can only be satisfactorily demonstrated by 

 means of sections. The sense organs, too, have an epiblastic 

 origin. 



ProsobrancJdata. — The 'prevalence of westerly storms when I 

 was at Naples gave me an opportunity of examining Janth'mo, 

 fragiUs. The ovum, which is crowded with coarse yolk sphe- 

 rules, divides into four segmentation spheres in the ordinary 

 manner. Fig. 6 shows the next stage, the four new epiblast 



be found in vol. i, p. ] 89, of the late Prof. Balfour's ' Treatise on Com- 

 parative Embryology.' I cannot refrain from here acknowledging my 

 great indebtedness to my late beloved master and friend. 



1 S. L, Lovcn, "Vetensk. Akad. Handl.," 1848, translated in 'Arch. 

 f. Nat.,' XV, 1849. 



' H. de Lacaze Duthiers, ' Ann. d. Sci. Nat,,' 4th ser., vii, 1857. 



3 S. L. Loven, ' (Efversigt Vetensk. Akad. Eorhandl.,' 1844. 



■* H. Fol, ' Arch. d. Zool. exp. et gen.,' v, 1870. 



^ Ibid., iv, 1875. 



« E. ttay Lankester, ' Phil. Trans.,' 1875 (pi. x, fig. 8). 



