AJSURIDA. 427 



indications of very considerable specialization are 

 exhibited in the concentration of the nervous system, in 

 the mouth-parts being insunk within the head capsule, 

 in the structure of the springing organ and the ventral 

 tube, and in the reduction of the number of abdominal 

 segments to six. 



Summing up, it may be said that the Collembola 

 show certain features in which they resemble the 

 Thysanura on the one hand and the lower Arthropoda on 

 the other while, at the same time, they have undergone 

 very considerable specialization along lines of their own. 

 There do not appear to be any grounds for regarding them 

 as being degenerate animals. If the results of future and 

 more extended investigations definitely establish that 

 none of the Collembola have more than six abdominal 

 segments present in the embryo, their relationships with 

 the Thysanura and the rest of the Insecta will probably 

 prove to be much more distant than is implied by the 

 above remarks. It would assuredly be a sufficiently 

 fundamental character to separate them as a group from 

 all other Insects. 



VIIL— MARINE IXSECTS.* 



Contrary to what is usually believed among 

 naturalists, a considerable variety of insects are known to 

 inhabit the sea-shore below high-water mark, and to 

 undergo daily submersion during one or more periods in 

 their life-history. Very little attention, however, has 

 been devoted to them at present, and most probably a 



* The term "marine" is only strictly applicable to insects in a 

 very limited number of instances. Although many of the species 

 included in the above account undergo frequent submersion by the 

 tide during one or more periods in their life-histories, others do not, 

 and are more strictly speaking to bo regarded as " littoral " insects. 



