KOFOID: DEVELOPMENT OF LIMAX. reti 
(labelled e by Blochmann) also precedes in somo instances in the later 
divisions. The yolk, however, is confined mainly to two of the macro- 
meres, A and B, instead of being lodged principally in three, A, B, and 
C, as it is in Umbrella. 
All attempts to reconcile the cleavage of Chiton, as described by 
Kowalevsky (083) and Metcalf (93), with the alternation of spirals 
shown in other forms of Molluscan cleavage are involved in serious 
difficulties, Unfortunately neither author figures nuclei or spindles, 
with the exception of one figure in each paper. The relationship of 
cells and the direction of the spiral is also explicitly stated in certain 
cases to be a matter of conjecture on their part. Therefore it does not 
seem profitable for me to add to their conjectures others of my own. 
It is however possible to force upon the cleavage of Chiton, as figured 
by these authors, an interpretation which causes it to accord with the 
spiral type of cleavage, but this interpretation meets a serious obstacle 
in the sixteen-cell stage, though it does not violate the relationships 
of cells in the few cases where these authors have indicated relation- 
ships by nuclear conditions (Kowalevsky, Plate I. Fig. 7, Metcalf, Plate 
XV. Fig. xvii.). 
I do not wish to commit myself to the view that Chiton conforms to 
that type, for, as Metcalf has suggested, * most of the divisions are 
of the radial type." The distribution of the yolk in the blastomeres is 
also suggestive of the radial type. There are, however in Kowalevsky's 
figures (Plate I. Figs. 4-13) many suggestions of spiral cleavage. In 
Motoalf's figures, on the other hand, “individual variations in the shape 
of the blastomeres are not preserved. The figures show what may be 
called the typical condition.” Thus most of the evidence of spiral 
cleavage, if such exists, must be eliminated from his figures. 
The cleavage of Discocalis conforms to the Spiral type and the alter- 
nation of spirals, with the possible exception of the spiral of 7.15-7.16, 
to which reference was made in my former paper (94, p. 196). It is 
necessary to relabel Figure 6 of Lang’s Tafel XXXV., in order to reconcile 
it with the apical views which he has given of the same stage, and also 
with the principle of alternation. 
The conformity of the cleavage of Nereis to the law of alternation of 
Spirals is perfect, as is demonstrated by the application of the uniform 
system of naming spirals in the above table. Even in those eleavages 
designated as equatorial or meridional, traces of the spiral characteristic 
of the generation can often be detected. 
The Nereis table is marked by the abrupt-termination of the Spiral 
