GENERATIVE ORGANS OF ARTHROPODA. 305 



or shorter and grouped into tufts, or branched tubes; they are 

 attached to the efferent ducts at various points. 



The male copulatory organs of the Insecta resemble the female 

 ones, and are made up of chitinised ridges and valve-like arrange- 

 ments, which vary greatly in fonn, and surround the generative 

 orifice. They are divided into those which serve only for external 

 copulation, and into others which are comparable to a penis, and are 

 capable of intromission. The latter are formed by a tube, which is 

 either attached externally, oris protrusible ; the ductus ejaculatorius 

 is continuous with it, and it often carries pincer-like organs at its end. 

 In the Ooleoptera this copulatory organ is enclosed by a thick-walled 

 chitinous capsule placed in the abdomen, which is often of consider- 

 able size, and is provided with a special muscular apparatus to 

 protract it, and draw it in again. 



§ 237. 



The seminal elements of the Crustacea, though very variable in 

 form, always agree in being motionless; the seminal filaments of 

 the Cirripedia are an exception to this. Although the seminal 

 elements are filamentous in the Isopoda, Amphipoda, and Ostracoda, 

 they are incapable of movement ; in the last-mentioned group they 

 are extraordinarily long. Among the Schizopoda, in Mysis, at least, 

 they are filamentous, and are bent at one end so as to form a hook. 

 Cell-like bodies are the most common forms ; owing to the presence 

 of processes they present various peculiarities, the most notable of 

 which is the radiate form of the semen of the Decapoda ("radiate 

 cells "). The seminal filaments also of many Arachnida and Myria- 

 poda appear to be incapable of movement, although in the former 

 they are motile, when within the female generative organs. 



In the Insecta the form-elements of the sperm are movable 

 filaments, which are generally drawn out into a process at either end. 

 The union of these filaments into tufts is an arrangement peculiar to 

 them, as is also the union of the cells in two rows to form a rod-like 

 structure which resembles in character a spermatophore (Orthoptera). 



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