No. 598] CHROMOSOME STUDIES ON THE DIPTERA 589 



Certain recurring kinds will be distinguished in advance 

 and will be designated byname or letter in the specific 

 descriptions. These are as follows : 



V. Long, V-, U-, or dumb-bell shaped chromosomes, 

 attached to the spindle at the median const ricted 

 portion (apex of the V). 

 r. Eod-like, straight chromosomes, approximately 

 half the length of V, attached to the spindle at 

 one end, and radially arranged in metaphase. 

 c. Short, curved chromosomes, differing from r only 

 in form and (probably) in having a median at 

 tachment to the spindle. 

 m. 3 Minute, spherical or slightly elongate chromo- 

 somes, usually located in the center of the meta- 

 phase plate. 



To these symbols must be added XX and XY, used to 

 designate the sex chromosomes wherever they have been 

 definitely identified. In some species they are straight, 

 in others Y-shaped. Identification of the sex chromo- 

 somes and determination of the XY relations in the males 

 has been one of the most difficult features of the study, 

 owing to the extreme scarcity of spermatogonial and 

 spermatocyte figures; but it has been made in as many 

 cases as possible and has been of great usefulness in 

 comparing different groups. 



The order or sequence in which the types are described 

 is a purely arbitrary one, and is not intended to indicate 

 any genetic relationship. 



groups which have previously been described and figured 



terest. The series of types as a whole may best be under- 

 stood from an examination of diagrams A to L, which 



types. 



