S92 COMPAEATIVE ANATOMY. 



evidently a compact germ-gland (Fig. 152, a), from which an 

 efferent duct (6) passes off on each side. We find this arrangement 



of the germ-gland in the Branchiata, 

 and in some of the Tracheata (Ar- 

 achnida). In almost all the Crus- 

 tacea the efferent duct is completely 

 double as far as its orifice {A). The 

 '^ ^ same arrangement obtains in the 



Mg is^i. Diagrams of the cliaractcrs Myriapoda, among the Tracheata. 

 or the generative system lu the .,.,'' ^ -^ , ,9 . , -, -i • 

 Arthropoda. a Germ-glauds. tcEffie- The germ-gland begms to be dl- 

 rent duct. vided among the Crustacea. The 



oro-an is then divided between its 

 two efferent ducts (Insecta). The approximation of the orifices 

 leads to the formation of a common orifice, and this to the forma- 

 tion of an unpaired portion of the duct (c). In many Arachnida 

 this azygos tract is connected with a circular part, more or less 

 of which is formed by the germ-gland (0). The ring is then formed 

 by an inherited (primary) stage— the single germ-gland — and by an 

 acquired (secondary) stage — the fused part of the efferent ducts. 

 While the generative glands of the Crustacea form the lowest grade 

 of this series, the Insecta appear to form the highest, for, owing to 

 the bilateral separation of the germ-gland, and the terminal fusion of 

 the efferent ducts, and the formation of a common unpaired portion, 

 they are the farthest removed from the lowest stage (D). The 

 germ-glands, as well as the efferent ducts, may undergo various 

 differentiations : especially the ducts, of which sometimes the paired 

 and sometimes the unpaired portion is affected. Except in the 

 fixed Cirripedia, impregnation is effected by copulation. In corre- 

 spondence with this there is a space formed near to, or at some 

 distance from, the terminal portion of the female efferent duct, 

 from a diverticulum of a division of it ; this (receptaculum seminis) 

 serves to take up the sperm, and may be converted into appendices 

 of a more independent character. Lastly, there is a bursa copulatrix 

 for the reception of the penis. 



The organs which serve to protect the eggs after they have 

 passed out of the body are of many kinds. Some of the appendages, 

 in the Crustacea especially, are often metamorphosed in this direc- 

 tion. Even whole regions of the body may be converted into 

 mai'supial pouches. Much of the difference between the male and 

 female individuals is due to these relations to the care of the young. 

 Finally, the number of eggs pi-oduced is an important element in 

 modifying all parts of the female apparatus; for not only the enlarge- 

 ment of the efferent spaces, but the various changes of all the accessory 

 organs, and, again, the increased size of the female are all due to the 

 production of a large number of eggs. 



The organs necessary for copulation, as well as the differentiations 

 which affect the efferent ducts, lead to complications of the male 

 apparatus. When the protractile end of the efferent ducts does not 

 serve in copulation, there are special copulatory organs, which are 



