mVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 239 



— projects a narrow strip of its tissue into the mantle fold. The 

 origin of the mouth was not observed. 



It seems reasonable to conclude that the ciliated zone is homo- 

 logous with that of Chilostomatous larvjc, to whose " hood," also, the 

 ectodermal thickening seems comparable. 



Arthropoda. 



Locomotion of Insects and Arachnida.* — The mode of progres- 

 sion of Insects and Arachnida is, according to M. G. Carlet, much 

 more regular than is generally supposed. The only rule laid down 

 by authors is that two legs of the same pair never move simul- 

 taneously. 



Insects whose movements are slow and whose legs are equi- 

 distant (as Orydes nasicornis and Timarcha tenehricosa), move tlieir 

 limbs as indicated in the following tabic, where the legs are arranged 

 in their natural position, the figures indicating the order in which 

 they are raised : — 



1\ 4 



While the legs 1, 2, 3 are raised almost together, 4, 5, 6 remain 

 as the support, to be raised in their turn when the first have resumed 

 the oifice of supporters. In other words, the insect rests on a triangle 

 of support formed by the two extreme feet on one side and the middle 

 one on the other side, whilst the other three feet are carried forward. 



This mode of progression equally obtains in the other orders. 



In arachnids the order in which the feet are raised was clearly 

 followed in the female of Epeira diadema. It is almost im2)ossiblc to 

 trace it out in the males on account of their rapid motion ; but the 

 more voluminous abdomen of the females hinders their progress and 

 renders it possible to construct the following table: — 



Here the polygon of support is a quadrilateral formed on the 

 one side by the feet of even numbers, and on tho other by those of 

 odd numbers. 



a. Insecta. 



Beetle with Proboscis of Butterfly.f — llcrr Hermann Miiller, in 

 contiasting tho ditlcrent states of dtjvuloj)ment which tlie j)art9 of tlio 

 mouth attain in the groups Apidic and Ivhopalocera (IJcesand JJutter- 

 flies), j)oiiit8 out tliat tlio limitation of tlieso parts to little more tlian a 

 long tube in tlie latter, and their extension in tho former to a complicated 



» 'Curnplcs Rcii.his,' Ixxxix. (1879) p. 1121. 

 t ' KosmoH,' iii. (1880) |). :^02. 



