108 PROGRESS OF MICROSCOPICAL SCIENCE. 



though thui'o ia a very slight tendency towards the iinilatcrality of 

 Myriopods in the male organs. 



" To Insects, again, it is allied by the five-jointing of the feet and 

 oral jiapillfc and the form and number of its claws. It should be 

 remembered that spiders' feet are two-clawed, as are those of some 

 Tai-digrades, and that some of these latter forms have two-clawed 

 feet in the early condition even when they possess more claws in the 

 adult state. In Newport's well-known figure of the young lulus 

 with three pairs of limbs, the tips of these latter are drawn with 

 two hair-like claws ; these are not mentioned in the text. To the 

 ordinary lepidoi>tcrous larva the resemblances of Peripatus are striking 

 — as, for example, the gait, the glands (so like in their function and 

 l^osition to silk-glands), the form of the intestine, and the less perfect 

 concentration of the nervous organs, as in larval insects. To Myrio- 

 jiods Peripatas is allied by the great variety in number of segments in 

 the various species, in its habits, and in these especially to lulus. 

 Tlie parts of the mouth perhaps show a form out of which those of 

 Scolopendra were derived by modification ; but the resemblance may 

 be superficial. Our knowledge is not yet sufficient to determine such 

 points. The usual difficulties occm* in the matter. Segments may 

 have dropped out or fused, and their original condition may not be 

 represented at all in the process of development. In structure Peri- 

 jyatus is more like Scolopendra than lulus, viz. in the many joints to 

 the antennae (in Chilognaths never more than fourteen), in the form 

 of spermatozoa, and in being viviparous, as are some Scolopendrce ; 

 further, in the position of the orifices of the generative glands and in 

 the less perfect concentration mesially of the nerve cords in Scolo- 

 pendra. 



" Peripatus thus shows affinities, in some points, to all the main 

 branches of the family tree of Tracheata ; but a gulf is fixed between 

 it and them by the divarication of the nerve cords : tending in the 

 same direction are such facts as the non-striation of the muscles, the 

 great power of extension of the body, the arrangement of the digestive 

 tract in the early stage, the persistence of metamorphosis, and the 

 nature of the parts of the mouth, the full history of the manner of 

 origin of these being reserved. 



"There are many speculations as to the mode of origin of the 

 trachea) themselves in the Tracheata. Professor Hackel * follows 

 Gegenbaur, whose opinion is expressed in his ' Grundziige der verglei- 

 chenden Anatomic,' ]). 441. Gegenbaur concludes that tracheae were 

 developed from originally closed tracheal systems, through the inter- 

 vention of the tracheal gills of prima3val aquatic insects now repre- 

 sented as larvse. If Peripattis be as ancient in origin as is here 

 supposed, the condition of the tracheal system in it throws a very 

 different light on the matter. Peripatus is the only Tracheate with 

 tracheal stems opening diffusely all over the body. The Pro- 

 tracheata probably had their tracheae thus diffused, and the separate 

 small systems afterwards became concentrated along especial lines 

 and formed into wide main branching trunks. In some forms the 

 * ' Biologische Studien/ p. 491. 



