420 SUMMARY OF CUERENT RESEARCHES RELATING TO 



details as to peculiarities observed in some of the groups, and as to 

 the opinions of some of the numerous other investigators of this 

 subject are discussed. 



(a) Biidiment of the sexual organs. — The first rudiment of the 

 sexual organs appears as a muscle-fibre which branches ofl' from an 

 alary muscle. It is inserted posteriorly and anteriorly on the 

 hypodermis. An accumulation of nuclei forms a median swelling, 

 which is defined off from the anterior and posterior terminal threads, 

 which ho terms Miiller's filament and the primary efferent duct 

 respectively. Both of these exhibit nuclei, especially the latter, but 

 both may be structureless. 



(6) Nuclei of the genital rudiment and efferent duct. — The germinal 

 epithelium is not definitely cellular, but consists of nucleated proto- 

 plasm. These nuclei are of two kinds, spherical and vesicular. The 

 former are larger and probably originate from the latter, from which 

 they difier in the disposition of their nuclear fluid. Both divide, and 

 from such nucleated protoplasm not only the sexual rudiment, but the 

 so-called duct of Herold are formed. By mutual pressure the large 

 nuclei become polygonal, and form the well-known epithelium of the 

 ovarian tubes, which is thus not strictly composed of cells. The 

 smaller nuclei usually become squeezed in interspaces, and have been 

 described as amoeboid " wandering cells." 



(c) Direct development of the reproductive rudiment. — (1) In the 

 viviparous Cecidomya larvae, in Collembola, Gampodea, Coccus, Lecanium, 

 Aspidiotus, and male Diptera, the reproductive rudiment forms the 

 sexual organs directly. In the Podurse the ova and " spermatoblasts " 

 arise directly from the differentiation of cells from the large spherical 

 nuclei of the protoplasmic mass. In other cases a simple terminal, 

 or a manifold yolk-chamber is formed. In the female Coccus, Leca- 

 nium, and Aspidiotus, lateral germinal tubules are formed, while the 

 median portion of the rudiment remains as the efferent duct. (2) In 

 all other insects the sexual organs are formed from a differentiation 

 of the rudiment, within which long round tubules, limited by a mem- 

 brane, are formed. These usually lie, at first, at right angles to the 

 longitudinal axis of the rudiment, but in most cases they afterwards 

 radiate out in fan-like fashion from the secondary efferent duct. The 

 envelope of the rudiment persists for a while as a structureless mem- 

 brane with an apposed nucleated layer of protoplasm, but is in most 

 cases absorbed before the imago is perfected, though remaining as the 

 muscular egg-sac in Diptera, and as an interrupted, nucleated, net- 

 like membrane in Blattidee and Saltatoria. A peritoneal envelope is 

 formed round the tubules, and another portion of the protoplasm forms 

 special terminal filaments, connecting the ends of the tubules with 

 Miiller's filament. The secondary efferent duct appears and remains 

 in Orthoptera, Thysanura, Thyrepsida, and Hemiptera ; appears and 

 disappears in Diptera ; while in Coleoptera, Hymenoptera, Neuroptera, 

 and Lepidoptera, it is not formed at all, the tubules coming into direct 

 connection with the primary efferent duct. In the males the peri- 

 toneal sheath and the special terminal filaments are generally absorbed, 

 and the tubules become spherical. The primary efferent ducts unite 



