KOFOID: DEVELOPMENT OF LIMAX. 65 
was able to assign a definite fate to each blastomere; 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 tablo 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, therefore, 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 treated in as brief a form as possible 
the discussion of each case is accompanied by a tabulated presentation 
of the clenvage, in which the author's designation of cells and spirals is 
joined in parallel 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 I 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 cleay- 
age as Cavolina, and his few figures of the early stages of this form 
suggest that 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 typo, Pterotrachea 
(Plate IV. Figs. 5, 6) the reversed type, if his labelling, 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. XXVII. — NO. 2, 5 
