DEVELOPMENT OF THE GENERATIVE ORGANS. 693 
can be investigated in a single section. Even as early as the 
eighth day of the pupa the posterior half of the testis—that 
nearest to the duct—is found full of half-formed bundles of 
spermatozoa; whilst the cells in its fundus remain unaltered. 
These unaltered cells, or mother-cells, I shall term spermato- 
spores, using the nomenclature adopted by Gilson [357]. 
The Spermatospores apparently undergo many divisions, and 
originate from a few primordial cells. In young males, a few 
hours after their escape from the pupa, many of these sper- 
matospores still remain near the fundus of the organ. They 
are precisely similar to the cells found in the young testis on 
the third day of the pupa stage. 
The spermatospores average from 7 » to 8 in diameter, 
and have a granular appearance; they are polyhedral in form, 
and are arranged in groups. Each group is sometimes sur- 
rounded by a thin capsule, so that it appears as if the final 
stages of multiplication take place by endogenous cell divi- 
sion; i.c., a portion of the protoplasm of the mother-cell 
remains as a capsule, enclosing a number of daughter-cells. 
Origin of the Primordial Sexual Cells.—All attempts to trace 
the origin of the first cells, from which the mother-cells are 
derived in the Muscide, have hitherto failed ; but the earlier 
stages of spermatogenesis in the Blow-fly pupa and the im- 
mature imago are so precisely similar to those described by 
Hertwig [856] and Lee [858] in the Chetognatha, that it may 
probably be assumed they originate in a similar manner. 
According to Lee, Sagitta bipunctata offers exceptional facili- 
ties for the investigation of the origin of the primordial sexual 
Bibliography : 
355. BUTSCHLI, O., ‘ Niihere Mittheilungen iiber die Entwicklung und den 
Bau der Samenfiiden der Insecten.’ Zeitsch. f. w. Zool., Bd. xxi., 
1871. 
356. HERTWIG, O., ‘Die Chetognathen.’ Jena, 1880. 
357. GILSON, G., ‘Etude comparée de la Spermatogéndse chez les 
Arthropodes ’ (3me partie, conclusions). La Cellule, tom. iv. (1887), 
1889. 
358, Ler, A. BOLLES, ‘La Spermatogéntse chez les Chétognathes.’ La 
Celiule, tom. iv. (1887), 1889. 
