522 MR. F. E. BEDDARD ON THE DEVELOPMENT AND [DeC. 7, 



Ceratodus, is the resultant of a large number of cells the protoplasm 

 of some of which undergoes certain changes and forms a more or 

 less fluid mass with the original nuclei suspended in it ; this mass 

 appears around and between the rest of the cells, which are destined 

 for its nutrition. The whole structure is surrounded by a definite 

 follicular layer, which also shares in its nutrition by the formation of 

 yolk in its cells and their prohferation inwards. These bodies are 

 surrounded by cellular layers which correspond exactly to the layers 

 which surround the ova of other vertebrates ; the difference is that 

 instead of there being a single cell which grows at the expense of the 

 rest, the interior of the mass is formed by numerous cells, all equi- 

 valent. 



The bodies may be distinguished as multicellular or plasniodial 

 from the ordinary unicellular ova. The share which the follicular 

 epithelium takes in the nutrition of the ovum, I have discussed in 

 detail in my former paper and need not refer to it again here, except 

 to remark that the elaboration of food-material in the follicular layer 

 and its absorption by the ovum has of course no relation whatever 

 to my view that the ovum is a cell-complex. Certain writers have 

 adduced arguments of this kind as a disproof of the unicellular nature 

 of the ovum, which to my mind have no force. 



On the other hand, the developmental facts with respect to the 

 cells within the follicle appear to me to be diiBcult to interpret 

 otherwise than on the assumption that the ovum has the value of 

 more than a single cell. 



It is true that I have been unable to detect any earlier stages than 

 the one figured on Plate LII. fig. 1 ; but the intermediate stages 

 between that and the mature ovum are fairly complete. The dis- 

 covery of the earlier stages is of great importance ; it would decide 

 among others the very important question whether the central mass 

 of cells is, or is not, derived from primitive ova recognizable as such 

 in the germinal epithelium, and whether or not the central mass of 

 cells is formed by the migration inwards of a number of these cells 

 or by the repeated division of one. But, whatever may be the 

 answer to these questions, I have, I think, proved that the ovum is 

 formed out of this central mass of cells. Some of these cells are 

 apparently used as pabulum, but others fuse together into a mass 

 of semifluid substance, which bears a very close resemblance to the 

 liquor foUiculi of the mammalian follicle. The resemblance is still 

 more striking if we accept Waldeyer's statements that the liquor 

 foUiculi is produced by a direct metamorphosis of the foUicular cells, 

 their nuclei remaining, as in the case of Protopterus, suspended in 

 it. This substance, however, in Protopterus has not a mere passive 

 function, serving, as in the mammal, to aid in the expulsion of the 

 ripe ovum, possibly also in its nutrition; it retains the activity of the 

 cells from which it is derived and secretes yolk ; it must therefore 

 be looked upon rather as a plasmodium of these cells than a product 

 of their degeneration, although its deep staining with borax carmine, 

 as opposed to the very light staining of the remaining cells, indicates 

 some chemical change. Furthermore, there is no evidence of any 



