50 STRUCTURE AND PHYSIOLOGY 



instead of being a shapeless transudation from its body, is formed by successive 

 additions of epidermoid membranes applied over each other in proportion as 

 they are successively ossified. 1 have pointed out also that these polypi are 

 merely microscopic fixed Cephalopodes, having, hke the large species of this 

 genus, a bag which is contained within the tube, an excrementitial funnel, ovaries, 

 an intestinal canal with similar curvatures, and a head with all its aecessories 

 equally corresponding ; so that, if the Sepia, for example, instead of having the 

 dorsal part of its large bag ossified, had undergone the same change over the 

 whole external circumference of this organ, and if its base had been fastened by 

 an adhesive substance to a rock, it would have been exactly a gigantic polypus." 

 — New System of Org. Chem. p. 281-2. — Obs. The species on which Raspail 

 made these curious observations are not mentioned in the work from which the 

 extract is taken : they are applicable only to the ascidian polypes, and were 

 indeed derived from the Alcyonella stagnorum, as we learn from his Memoir on 

 this species in the fourth vol. of " Mem. Soc. Hist. Nat. de Paris." 



2. Dr Grant's Account nf the Ova of the Fhistra. 

 " Although the ova of Flustrae have been often observed, no one appears to 

 have hitherto examined either their mode of formation within the cells, or their 

 mode of developement after expulsion, so as to determine the real nature of these 

 globular bodies, and the erroneous conjectures of naturalists respecting them have 

 greatly perplexed the history of this genus. The ova of the F. carbasea make 

 their first appearance as a small yellow point, a little below the aperture of the 

 cell, and behind the body of the polypus ; they are unconnected with the poly- 

 pus, and appear to be produced by the posterior wall of the cell, in the same man- 

 ner as the axis, or common connecting substance of the polypi, produces them in 

 other zoophytes. In this rudimentary state, they are found in the same cells 

 with the healthy polypi, but, before they arrive at maturity, the polypi of such 

 cells perish, and disappear, leaving the entire cavity for the developement of the 

 ovum. There is never more than one ovum in a cell, and it occupies about a 

 third of the cavity, when full grown and ready to escape. When first visible, 

 it has a round or slightly oblong and regular form ; when mature, it is ovate with 

 the small end next the aperture of the cell. The ova do not appear in all the 

 cells at one time, nor is there any discernible order as to the particular cells 

 which produce ova, or the part of the branch which contains them. Cells con- 

 taining ova are found alike on every part of the branches, from the base to with- 

 in two or three rows from the apex, occupied only by young polypi. Some- 

 times we find half a dozen or a dozen of contiguous cells all containing ova, 

 sometimes two or three only ; and often such cells occur singly, at short and 

 irregular distances from each other. We find the ova in all stages of maturity 

 on the same branch at the same time ; and we seldom observe a specimen of 

 the F. carhasea, during the months of February, March, and April, which does 

 not contain numerous ova. The ova have a lively yellow colour ; and when 

 they occur abundantly on a specimen or a part of a branch, they cause it to ex- 

 hibit the same lively hue, which is very dilferent from the dull spotted brown 

 appearance which the branches present at other seasons. Cells are often ob- 

 served on different parts of the branches, containing neither polypi nor ova ; but 

 the fewness of these, and the great lumiber of cells still containing only polypi 

 at the season of generation, render it probable that polypi are regenerated in the 



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