GEN'ERATIOX OF INSECTS. 395 



side of the bead. Early in June, it has acquired twelve segments, 

 and eight pairs of legs, and the head presents three ocelli on each 

 side. Later, in the same month, the segments have increased to 

 fifteen, and the legs to fifteen pairs, and the number of ocelli is eight; 

 finally, two more segments are added, and the cluster of ocelli 

 includes twenty on each side. The chief distinction between the 

 Lithobius and lulus appears to be, that the successive joints are not 

 developed, as in the lulidce, at the posterior part of the body, from 

 one particular germinal space, but at the interspaces of the pre- 

 existing segments. 



With regard to the affinities of the Myriapoda as they are il- 

 lustrated by the known phenomena of their development, we discover 

 in the peculiarly localised power of superadding the additional joints 

 in the lalidiE, a marked analogy to the anellids ; yet the appendages 

 of the segments being distinctly jointed limbs, we have in these a 

 well-marked character of the superiority of the Chilognatha. Then, 

 in reference to the Crustacea, which the Myriapoda more resemble 

 in their jointed antennaj and limbs, we perceive also an interesting 

 additional resemblance in the Chilognatha, in the circumstance of the 

 organs of the generative apparatus not terminating in the homolo- 

 gous segments in the male and in the female ; whilst in both they 

 are situated nearer the anterior part of the body. But this crus- 

 taceous character disappears in the Chilopoda. And when we per- 

 ceive that the first form of the articulated animal with jointed limbs, 

 which the Myriapoda assume, is that of the hexapod insect, and 

 further, that in departing from this type, the pair of limbs succes- 

 sively added in the lulus are, like the temporary ones in caterpillars, 

 of a different character from the primary six, — we cannot but derive 

 from these facts a well-founded confidence in the importance of that 

 character of the respiratory system which associates the Myriapoda 

 with the Insecta rather than the Crustacea. 



I proceed now to demonstrate the structure and modifications of 

 the organs or instruments subservient to the formation, retention, 

 nourishment, defence, and transmission of the sperm-cells and germ- 

 cells, and their products or developments, in the true or hexapod 

 Insects. 



In entering upon a review of the structure of the male organs of 

 insects generally, we found their simplest type in the lowest or- 

 ganised members of the class, viz., the chilognathic myriapod?. 

 The testes and their ducts, with short and simple intromittent 

 organs, alone existed ; there were no accessory glands, no me- 

 chanical adjuncts in relation to the coitus. The sexual apertures, 



