kofoid: development of limax. G5 



was able to assign a definite fate to each blastomerc ; but in Limax 

 there is no trace, save in the early differentiation of the mesoderm, of 

 that precocious development so marked in Nereis. This fact makes the 

 identity of the cleavage of Limax with that of Nereis all the more won- 

 derful and difficult to explain. 



I insert here (p. 66) a table of the cleavage of Limax, so far as I have 

 followed it, which epitomizes the foregoing discussion of the alternation 

 of spirals in successive generations of cells. The spirals, wherever they 

 occur, conform to the law of alternation as defined in my former paper 

 ('94, p. 189). 



C. Literature on Spiral Cleavage. 



The conformity of other animals to the law of spiral cleavage has in 

 all cases been obscured by the systems of nomenclature employed. 

 Since no one of my predecessors has formulated this supposed law, it of 

 course has not been tested on any of the forms whose cleavage has been 

 worked out. It has seemed desirable, therefoi-e, to go over the available 

 literature and point out those cases which agree, and those which seem 

 to disagree with my proposition. 



In order that the subject may be ti-eated in as brief a form as possible 

 the discussion of each case is accompanied by a tabulated presentation 

 of the cleavage, in which the author's designation of cells and spirals is 

 joined in pai'allel columns with the designation which my system would 

 impose. 



In my former paper ('94, pp. 192-196) the conformity of the cleavage 

 of Neritina, as described by Blochmann ('81), to the alternation of spirals 

 was discussed, and the cleavage tabulated. In what follows 1 have 

 discussed all other cases which seemed worthy of consideration in this 

 connection. 



Fol states ('75, p. 117) that Clio likewise has the same regular cleav- 

 age as Cavolina, and his few figui-es of the early stages of this form 

 suggest tliat the cleavage is of the normal type. Cymbulia also seems 

 to conform to this type. 



The cleavage of the Heteropods, which he ('76) states is identical 

 with that of the Pteropods, is, according to his figures, of two types : 

 Firoloides (Plate I. Figs. 1-3) presenting the normal type, Pterotrachea 

 (Plate IV. Figs. 5, 6) the reversed type, if his lahelling, indicating the 

 lineage, is correct. There is evidence, however, that some of the divis- 

 ions belong to the normal type (Plate IV. Fig. 9). 



VOL. XXVIT. — xo. 2. 5 



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