222 Dr Martin Barry on the 



and presenting zones, which grow paler and paler as they 

 extend over a larger surface. These markings on the shells 

 of eggs often present a curious resemblance to the ramifica- 

 tions of the pigmentum nigrum, proceeding from reproduc- 

 tive centres ; as in eggs of several of the Buntings. 



Fig. 52 in" Plate II. represents part of an ovum of the Com- 

 mon Leech. I would direct attention to the resemblance be- 

 tween it and what I believe to be corresponding parts in ova 

 of the Rabbit, figured by myself in the Phil. Trans, for 1839, 

 Plates VI. and YII., fig. 114, &c., bb, bb% and a.p. 



The long pellucid area a m in fig. 52 is the situation of the 

 future nervous ganglia in the Leech. Compare it with an 

 obviously corresponding area in my figures just referred to — 

 the situation of the future spinal cord. Again, the round iris- 

 like body at a, fig. 52, — so far in advance of the other parts in 

 its formation, — is the sucking apparatus of the Leech, en- 

 dowed apparently at this early period with suctorial power. 

 Compare it with the nucleus of my queen bee cell in the same 

 and preceding figures ; which nucleus I have always main- 

 tained to be the rudimental embryo in the mammiferous 

 ovum. 



But the figure from the ovum of the Leech was published 

 by Professor E. H. Weber in Meckel's Archiv, in 1828, — 

 many years before any thing was known of the physiology of 

 cells. It serves as an example of the importance of fidelity 

 in delineation ; for I do not think that now, with all our 

 knowledge regarding cells, we could give a drawing much 

 more satisfactorily representing them ; — at least on the same 

 scale. 



That ovum of the Leech, elliptical in form, had a length 

 not exceeding three Paris lines. Yet even at this early pe- 

 riod. Professor Weber noticed that the sucking property of 

 the iris-like body, a, had begun to manifest itself in alter- 

 nate contraction and dilatation of the central orifice ; the ef- 

 fect of which seemed also visible in the surrounding albumen. 

 Compare these facts with observations recorded by myself on 

 the nucleus, bb, in the mammiferous ovum ; remembering my 

 orifice in the nucleus of the cell, — and all that I have now 



