L1>'NEAN SOCIETY OF LONDON. 49 



onwards in the Elasmobranch direction with shagreen scales and 

 possibly jaws from the primitive agnathous condition. The 

 question of the interpretation of the lateral markings on some of 

 the head shields of these mailed lishes is a comparatively small 

 matter. Smith Wood\^•ard agrees with me that they show the 

 presence of segmentation in this region, but thinks they were 

 branchial segments ; in my opinion, judging from Ammoccetes, 

 they extend too far forward for branchiae, and I think they are 

 more likely to have been due to the presence of muscles supplied 

 by the trigeminal nerve. 



Coming to Lankester's speech I have a difficulty in finding any- 

 thing to answer in it ; he spoke of cryptograms and of Bacon and 

 Shakespeare : another suggestion akin to the diabolic ingenuity of 

 MacBride which hardly requires any further answer than I have 

 given. He said there was no resemblance between the lateral 

 eyes of Vertebrates and Arthropods, but that is not the point ; it 

 is not the dioptric apparatus upon which I was laying stress, but 

 the retinal arrangements. It was the resemblance between this 

 latter apparatus in the two groups upon which every observer 

 from Berger to Parker has laid stress. 



Finally, I come to the remarks of Dendy. He referred to the 

 drawing of the right pineal eye of Ammocoetes as drawn in my 

 book as a diagram. That is not so: the left half of the drawing is 

 from the actual specimen, the right half is ray interpretation of 

 the meaning of the appeai'ance seen. In my paper in the Q. J. 

 Micr. Science all the drawings are carefully drawn by Wilson from 

 the actual specimens and are not in any way diagrams. He 

 referred to the finding by Studnicka in the pineal eye of Amnio- 

 ccetes of certain cells which he called ganglion cells. They are 

 not arranged like an optic ganglion and are much more like the 

 cells described in the median eye of Limulus by Lankester and 

 Bourne, and called by them intrusive connective tissue cells. 

 What these cells are I do not venture to assert ; in any case they 

 are present both in the median eye of Limulus and of Ammocoetes. 

 As to Geotria, I have explained in my book that the cells grouped 

 round the atrium may be nerve-cells as asserted by Dendy, but 

 they are found along the nerve from the ganf/Uon hahenulce to the 

 eye. In the left eye of Ammocoetes the nerve has vanished and 

 cells of the gcDic/lion habenulce run right into the eye. It is 

 perfectly possible that Geotria represents an intermediate stage 

 of degeneration between that of the right and left eyes of Ammo- 

 coetes, especially seeing that a portion of the original cavity is cut 

 off to form the atrium by the massing of the cells in question. 

 As to the tube of the nervous system, Dendy, as well as all the 

 other speakers on that side, find it very convenient to leave out 

 the infundibular prolongation in their picture of the formation of 

 an epithelial tube, an unfortunate omission as it happens to be 

 the main point of my argument. Dendy's vie«- that the choroid 



LINN. SOC. PBOCEEDINGS. — SESSION 1909-1910. 6 



