172 BIOLOGICAL LECTURES. 



each of these seven chromosomes shortens up into a regular 

 dumb-bell shape. 



During these prophases the chromatin nucleolus decreases in 

 size, partly by the loss of the substance of the contained vacu- 

 ole, partly by a dissolution of a portion of its own substance ; 

 but a portion of it always remains, and this portion gradually 

 becomes dumb-bell shaped before the disappearance of the 

 nuclear membrane. The true nucleolus disappears completely 

 during the prophases. 



In the equatorial plate of the first reduction spindle lie the 

 seven chromosomes, and by their side the chromatin nucle- 

 olus, in every case easily recognizable by its much smaller size. 

 The seven chromosomes and the chromatin nucleolus are then 

 divided transversely in metakinesis, so that each daughter-cell 

 (second spermatocyte) receives seven chromosomes and one chro- 

 matin nucleolus. But in the second reduction division, unlike 

 the first, the chromatin nucleolus does not divide as a rule, but 

 is carried undivided into the one or the other spermatid. 



Thus it is that in the spermatocytes of Euchistus a whole 

 chromosome becomes metamorphosed into a chromatin nucle- 

 olus ; and from observations made by me upon another genus 

 of the same group, Anasa, it would appear that the chromatin 

 nucleolus has a similar origin here also. In the spermatocytes 

 of some other insects (Phalangopsis> Gryllus, and Harpalus) I 

 have found similarly staining structures (which in Harpalus 

 are attached to the true nucleolus, thus constituting a double 

 nucleolus), but in these objects have not yet traced their origin. 

 May it not be that chromatin nucleoli will be found to be of 

 general occurrence in the spermatocytes of insects, if not indeed 

 of other groups also? If this be proved to be the case, and 

 the chromatin nucleolus in all objects be found to be a meta- 

 morphosed chromosome, then the chromatin reduction in such 

 spermatocytes would be of a different character from that in 

 ovocytes and the whole problem be still further complicated. 



2. Hypodermal Cells of Carpocapsa. The budding extremi- 

 ties of the apple-worm, which is the larva of the moth Carpo- 

 capsa^ offer a beautiful object for the study of certain nucleolar 

 structures. The hypodermis covering the body consists of 



