596 PATTERNS AND PROBLEMS OF DEVELOPMENT 



trispermic eggs develop more nearly normally than others and may give 

 rise to complete embryos and larvae, but there is often regional cessation 

 of development and death of cells at some stage, and partial forms with- 

 out reconstitution result. With extreme polyspermy, most of the embryo 

 may die, or the egg may not cleave.^" Death of cells, of regions, or of the 

 whole embryo evidently results not from alteration of cleavage pattern 

 but from the anomalous relations of nuclei and cytoplasm, cells being 

 often multinucleate, and from abnormal and irregular distribution of 

 chromosomes by multipolar spindles. 



From the facts at hand it appears that dispermy, like centrifuging and 

 pressure, may alter cleavage pattern without essentially altering cyto- 

 plasmic developmental pattern but that normal development rarely re- 

 sults, either because of pathological condition of eggs permitting dispermy 

 or because of anomalies in chromosome distribution. Chromosome 

 anomalies may alter or even obliterate developmental patterns by altering 

 quantitatively or qualitatively the metabolism of cells or cell groups. 



DIFFERENTIATION WITHOUT CLEAVAGE IN ANNELID EGGS 



Unfertilized or fertihzed eggs of the annelid Chaetopterus subjected for 

 an hour to certain concentrations of KCl added to sea water may undergo 

 some differentiation without cleavage or nuclear division (F. R. Lillie, 

 1902). The ectoplasm becomes vacuolated, as does the ectoderm of the 

 trochophore, and in some cases a ring of large vacuoles girdling the egg 

 resembles the ring of large vacuoles in the normal prototroch. Motile 

 cilia develop on the whole or a part of the surface; and slow or active, but 

 apparently undirected, swimming may occur. The yolk becomes aggre- 

 gated into a dense mass in the interior, sometimes separated from the 

 outer layer by a space. Cytoplasmic divisions may take place, but the 

 nonnucleated masses apparently fuse again with the nucleated portion. 

 Cilia develop somewhat later in these forms than normally. 



Ciliation without cleavage and in one case a form with a girdle of cilia 

 resembling the prototroch have also been obtained by KCl treatment of 

 unfertilized eggs of the polychete Podarke (Treadwell, 1902). Unfertilized 

 eggs of another polychete, Amphitrite, treated with Ca(N03)2, KCl, or 

 CaClz or subjected to strong mechanical agitation, may also undergo dif- 

 ferentiation without cleavage and without, or with, nuclear divison, or 

 with few irregular or partial cleavages and few nuclei (J. W. Scott, 1906). 



In these three forms normal cleavage is typically spiral, but some dif- 



3° A. Brachet, 1910a, b, 1912; Herlant, 1911. 



