OCT 18 1899 



No. 5. — Observations on Non-sexual Reproduction in Dero vaga. 1 



By T. W. Galloway. 



CONTENTS. 



1. 



2. 



3. 



Introduction 115 



Structure of the non-dividing 

 Animal and the Formation of 

 Segments 116 



Position of the Bud-zone : Pri- 

 mary and Secondary . . . 117 



Relation of Budding to Forma- 

 tion of Segments 119 



Experiments on the Rate of 

 Budding 120 



Methods 122 



PAGE 



7. Histological Features of the 



Budding Process . . . . 122 



a. Ectoderm 122 



b. Entoderm 126 



c. Mesoderm 129 



d. Summary of Changes in the 



Formation of the Mouth 



and Pharynx 132 



8. Conclusions 134 



Bibliography 138 



Explanation of Plates 140 



1. Introduction. 



The worm upon which the present study is made was originally de- 

 scribed by Leidy ('80) as Aulophorus vagus. A more complete account 

 of the anatomy and histology by Reighard ('84) makes it apparent that 

 its divergence from the species of Dero is not sufficient to warrant the 

 establishment of a new genus. The sexual features which I have 

 recently had the fortune to observe confirm this view. 



The excellent work of von Bock ('97) on budding in Chsetogaster dia- 

 phanus, in which there is a review of the work of preceding authors upon 

 non-sexual reproduction in worms, renders it unnecessary for me to sum- 

 marize previous accounts here. His interpretations are, however, in 

 some respects so diverse from those of earlier authors as to make it 

 desirable that they should be tested in another group. Dero is one of 

 the most specialized of the Naidiform Oligochseta, and for this reason 

 presents certain interesting variations from the conditions encountered 

 in the forms that have been previously studied. 



In the autumn, from September to November, Dero vaga is found 

 abundantly in tubes formed of Lemna leaves, or other small light objects, 

 at the surface of water in the ponds and ditches in the environs of 



1 Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology at Harvard College, under the direction of E. L. Mark, No. XCIX. 

 vol. xxxv. — no. 5. 1 



