1916] Thoracic a?id Cervical Sclerites of Insects 47 



four pieces which he termed the aero-, pro-, meso-, and metas- 

 ternites. The aero and prosternites constitute the "sternum," 

 while the meso- and metasternites form the" " sternellum. " 

 With this as a basis Berlese accounts for the sclerites which 

 make up a typical thoracic segment in the following manner. 

 First, the epimeron became spHt off from the "tergite, " while 

 the leg appendage arose from a part of the " metasternite " and 

 later the trochantin, consisting of two pieces became split off 

 from the "sternellum," in the region of the coxa. Next, the 

 epimeron entered into the composition of the pleuron near the 

 coxa and the two "alar plates" at the base of the wings, 

 together with the spiracles, became detached from the " tergite. " 

 The "sternum" became split up into pieces to form the epister- 

 num and sternum. It is obvious that Berlese's theory is 

 untenable. Considered from an embryological and anatomical 

 point of view, it has no foundation whatever. 



The later writers, Crampton, '08-'09 and Snodgrass, '09-' 10, 

 think that the thorax of insects is composed of three segments. 

 This view is supported by embryology and anatomy and is 

 based upon facts, while all the composite segment theories are 

 more or less lacking in such support, are not always based upon 

 facts and consequently are untenable. 



Dr. Prell, '13, who has recently published a paper on the 

 Myrientomata, views the insect thorax as follows: In the 

 abdomen of Acerentomon, he finds that each segment is divided 

 into four rings, which are further subdivided into regions by 

 sutures. In the thorax of Eosentomon these rings are repre- 

 sented by a number of sclerites which have become more or less 

 displaced from the. ring arrangement, owing to the specialization 

 of the thorax for locomotion. The sternal region is composed 

 of four subdivisions, which he terms the aero-, pro-, meso-, and 

 metasternite. The tergal region is also composed of four sub- 

 divisions, the aero-, pro-, meso-, and metatergite and in addition 

 a region called the nototergite becomes secondarily marked off 

 from the metatergite. In the pleural region of each segment, 

 he finds two longitudinal rows of sclerites. Those bordering on 

 and extending along the lateral margin of each thoracic sternum, 

 he terms the sternopleura or pleura in the restricted sense. Those 

 which border on and extend along the lateral margin of each 

 tergal region , he terms the sympleura or tergal pleura. B oth sy m- 

 pleura and pleura are composed of four sclerites, lying one 



