114 COMPARATIVE ANATOMY. 



between the fasciculi of the cutaneous muscle,' communi- 

 cate with the general visceral cavity, the genital products 

 escaping thence through openings between the feet. (Siebold.) 



Crustacea. Generally unisexual; hermaphroditic forms 

 are seen with Cirripedia. Male and female organs, as a rule, 

 resemble one another. Great variety witnessed in the detail 

 of their arrangement in different families. The sexual ele- 

 ments are placed within simple tubes arranged bi-laterally, 

 and with comparatively few exceptions, open upon ventral sur- 

 face of animal by distinct pores. At the female genital pore a 

 special glandular canal is occasionally met with; a receptacle 

 for semen (spermatotheca) is rarely seen. The male pore is 

 commonly furnished with copulatory organs, in the form of 

 stylets or canaliculi, which serve to transfer the sperm to the 

 female. To these may be added the 'claspers,' which are 

 more remotely placed. In Homarus (lobster), the genital 

 pore in male is upon basal articulation of last pair of ambu- 

 latory feet; in other decapods the orifice is upon abdominal 

 surface of last thoracic ring. Copulation is common. 



Insecta. Always unisexual. The genital organs are com- 

 posed in general of two symmetrical ovaries or testicles, often 

 intimately resembling one another, situated in the abdominal 

 cavity, and of two oviducts or deferent canals, which unite in 

 a common excretory duct opening back of the anus or in it, 

 forming a cloaca. This duct has several double or single 

 appendages of which one, with the female, serves as a sem- 

 inal receptacle, or as a copulatory organ, while the others, in 

 both sexes, are true secretory organs. In the female the 

 vagina is often prolonged into an ovipositor. This may be 

 composed of segments which can be drawn within one an- 

 other, as in Diptera .(fly) ; or protected by two valvular pro- 

 jections which appear to prolong the body posteriorly, as in 

 Locustae (grasshopper).; or long, stout, and employed as 

 borer (tenebra), as in Cynipida3 (gallfly), slender and acu- 

 minate, and employed as sting (aculeus), as in Apidse (bee). 

 The same segment .modified in the male constitutes the penis. 

 It commonly opens on vcntrum at about the ninth ring. 

 The rseminal receptacle is .a double or single capsule of vari- 



