Mollusca. Echinoderma. 1 15 



sich hastig aus. Platzmangel und die dringende Erntearbeit hatten ihre kriegerischen 

 Instinkte modifiziert. Während der Beobachtungszeit vom 26. 6. — 31. 7. blieb das Bild 

 immer dasselbe. P- Schulze (Berlin). 



Hierzu: Nr. 123, 161, 162, 163, 177, 209, 227, 229, 243. 



Mollusca. 



305) Rubbel, A., Zur Kenntnis der Schalenregeneration bei der Flußperl- 

 muschel. In: Zool. Anz. 37, 8/9, S. 169—172, 1911. 



Experimentelle Untersuchungen über die Regenerationsfähigkeit der Flußperlmuschel 

 {Margaritana margaritifera) führten zu dem Ergebnisse, daß die äußeren Epithelzellen 

 des Mantels fähig sind, außer dem Perlmutter auch Periostracum und Prismenschicht zu 

 bilden. Anodonta cellensis scheint sich in dieser Beziehung ganz ähnlich zu verhalten. 



F. Pax (Breslau). 

 ^. Hierzu: Nr. 147, 164, 209. 



Echinoderma. 



306) Doncaster, L. and Gray, J. (Cambridge, University), Cytological 

 Observations on Cross-fertilized Ecliinoderm Eggs. In: Proc. Cam- 

 bridge Phüosoph. Soc. 16, 5, S. 415—418, 1912. 



Examination of segmenting eggs of the hybrids EcJiimis escülentus ? X 

 Echinits acutus J", acutus $ X escülentus c?, and acutus $ X miliaris cT, showed 

 that in the first-named the mitotic figures were quite normal, but in the first 

 segmentation division of acutus $ X escülentus cT and to a less extent in acu- 

 tus $ X miliaris c? some of the chromosomes swell up into vesicles. The whole 

 chromosome may be used up in forming a vesicle, or part of it may give rise 

 to a vesicle which is thrown off and the remainder then behaves normally. 

 The vesicles are frequently left on the edge of the spindle in anaphase, and are 

 not included in the daughter nuclei. Their number varies from one to nearly 

 a^dozen, and in anaphase groups of acutus $ X escülentus c? from 32 to 37 

 chromosomes were counted, the normal number for both the parent species being. 

 38. Similar but less pronounced vesicle-formation occurs in the second segmen- 

 tation division, but the acutus $ X miliaris c? cross indicates that it ceases in the 

 later divisions. Doncaster (Cambridge). 



307) Teniiant, D.H., The correlation between chromosomes and par- 

 ticular characters in hybrid Echinoid larvae. In: Amer.Nat. 46, S. 68 

 bis 75, 1912. 



This paper states some of the results of the study of chromosome behaviour 

 in Echinoids having certain chromosomes whose shape enables their history to 

 be traced in the segmenting eggs and larvae. It is found that half the sperma- 

 tozoa of Hipponoe have a hook-shaped chromosome which, when it fertilizes an 

 eggi produces a male. This dement is not present in Toxopneustes. In the cross 

 Toxopneustes X. Hipponoe it occurs in half the f ertilized eggs, while in Hipponoe X 

 Toxopneustes it never occurs. Another case, based on eggs of Toxopineustes straight- 

 f ertilized, artificially parthenogenetic eggs, f ertilized enucleated egg fragments, and 

 four Grosses, namely reciprocal Hipponoe X Toxopneustes and reciprocal ÄrbaciaX. 

 Toxopneustes, furnishes interesting data. Ordinary fertilized eggs of Toxopneustes 

 are of two classes, having, respectively, 2 and 3 v-shaped chromosomes. Partheno- 

 genetic eggs show only 2 v-shaped chromosomes, while fertilized enucleated egg 

 fragments show either 1 or 2. This is not in accord with the expectation from 



8* 



