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 /JL 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.e., 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 Muscidse, 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 [356] and Lee [358] in the Chaetognatha, 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., ' NahereMittheilungen iiber die Entwicklungund den 

 Bau der Samenfaden der Insecten.' Zeitsch. f. w. Zool., Bd. xxi., 

 1871. 



356. HERTWIG, O., 'Die Chaetognathen.' Jena, 1880. 



357. GILSON, G., ' Etude comparee de la Spermatoge'nese chez les 

 Arthropodes ' (3me partie, conclusions). La Cellule, torn. iv. (1887), 

 1889. 



358. LKE, A. BOLLES, ' La Spermatoge'nese chez les Chetognathes.' La 

 Cellule, torn. iv. (1887), 1889. 



