GENERATION OF INSECTS. 399 



ducts : re short, and receive the secretion of two long prostatic fol- 

 licles. 



In the order Orthoptera, we find the locusts with testes composed 

 of numerous blind tubes, in most species enclosed in a common 

 capsule ; and in some, e. g. the cockroaches {Blatta\ the testicular 

 follicles are collected into a common mass in the middle of the 

 abdomen. The prostatic glands also consist of fasciculi of tubes, and 

 remind us of the condition of the prostate in some rodentia. Their 

 secretion is moulded into spermatophora. 



The order Coleoptera offers the greatest diversity in the form 

 and structure of the male organs. In Dytiscus each testis is a 

 filiform tube, much longer than the abdomen, but convoluted into 

 a round ball. In Hydrophilus the gland is represented by a series 

 of short blind processes given off from one side of a common 

 sperm-duct. In Buprestis a fasciculus of longer caecal tubes radiate 

 from the end of the sperm-duct. Sometimes the extremities of 

 similar radiating tubes are dilated into sacculated flattened glands, as 

 in the rose-beetle {Cetonia), and numerous more composite forms have 

 been detected ; all, however, are referrible to modifications of the 

 primitive blind secerning sac. Their analogy to the sexual parts of 

 plants has already been alluded to, and entomologists have found it 

 requisite or advantageous to borrow the neat and descriptive terms, 

 with which Linnaeus has enriched botanical science, in order to in- 

 dicate the diversified forms of the male apparatus in the subjects of 

 their favourite class. The intromittent organ is a long horny tube ; 

 usually retracted within the abdomen, but not capable of retraction 

 after complete intromission, which usually terminates by rupture of 

 the organ. Hence the Coleoptera, like the Lepidoptera, are mono- 

 gamous. The terminal portion of the ejaculatory duct is continued 

 into the penis, and, in Carahus clathratiis, opens upon the centre 

 of a soft glandiform termination of the intromittent organ. 



Much unity of plan may be traced throughout the varied modifi- 

 cations of this organ in insects. In general terms, the intromittent 

 organ may be defined as a modification of the last, or two last, seg- 

 ments of the abdomen. It consists of a large exterior sheath and a 

 delicate membranous tube ; the sheath commonly consists of two 

 lateral valves. It is usually retracted out of sight. Accessory pre- 

 hensile organs are developed in some insects, of which the most re- 

 markable are those which are attached to the base of the abdomen 

 in the male Libellula. In this remarkable insect, the sperm-ducts 

 terminate, as usual, on the anal segment; but the vesicula seminalis 

 is situated at the base of the abdomen. The semen is transferred 

 thither by a strong inflection of the caudal end of tlie abdomen, prior 



