4 bulletin: museum of comparative zoology. 



II. Material and Technique. 



The material upon which these observations were made was obtained 

 from Scolopendra heros, the large centipede most common in the south- 

 western part of the United States. The greater part of the work was 

 done upon material obtained from Russel County, Kansas, in June, 1900, 

 through the kindness of Mr. W. S. Sutton. Later a number of speci- 

 mens of the same variety of S. heros were received from Beulah, Colorado, 

 through Mr. B.. E. Scammon. 



The testis of S. heros consists of a variable number of follicles lying 

 near the dorsal wall of the body-cavity and communicating with the ex- 

 terior at the hind end of the body by means of the vasa deferentia. 

 Usually the follicles are united in pairs to constitute a lobe, but occasion- 

 ally there is only a single follicle to a lobe. Each follicle is in effect a 

 blind tube, its only connection being with the vas deferens. 



The arrangement of the various cell generations within the follicle is 

 quite different from that existing in insects. This would naturally be 

 expected in view of the fact that the centipede is a perennial animal and 

 that the testicular elements must therefore be so arranged as to permit 

 the annual regeneration of the organ. The extreme periphery of the folli- 

 cle is occupied by spermatogonia in various stages of so-called rest and 

 of cell division (Plate 1, Fig. 1). In the mature testis these never 

 form a continuous layer. From the periphery to the centre of the folli- 

 cle, there are found in the order given : (1) young spermatocytes, of 

 many sizes and stages of growth, (2) spermatocytes in the " vesicle " stage 

 and in various phases of the maturation divisions, (3) spermatids in 

 different stages of metamorphosis, and (4), in the centre of the follicle, 

 mature spermatozoa. 



In a series of preparations made in June, about one half of the volume 

 of the follicle is occupied by spermatozoa. In preparations of ma- 

 terial, captured in August and September, the follicles are smaller and 

 the space occupied by spermatozoa is relatively somewhat less. It is 

 worthy of note that the follicles of the testis have not all developed at 

 the same rate, so that in the ripe testis all stages are abundantly 

 represented. 



In the preparation of the material two fixing fluids were used : Flem- 

 ming's chromic-osmic-acetic mixture and Gilson's nitric-acetic-sublimate 

 mixture. The results with Flemming's fluid, while fairly # good, were so 

 inferior to those obtained with Gilson's mixture, that in the later prepa- 

 rations the latter reagent was used exclusively. "With. Gilson's fluid 



