18 THE ANATOMY OF THE HONEY BEE. 



is no maxillary palpigor, but many insects i)()ssess a corresponding 

 part in the maxilla, frequently distinguished as the palfifer. 



The neck or cervicum is usually a short membranous cylinder which 

 alloAvs the head great freedom of motion u]wn the thorax. In nearly 

 all insects its lateral walls contain several small plates, the cermcal 

 sclerites^ while, in many of the lower species, dorsal, ventral, and 

 lateral sclerites are present and highly developed. As already stated, 

 the origin of these plates is doubtful. Some entomologists would 

 derive them from the prothorax, others think they come from the 

 last head segment, while still others think that they represent a 

 separate segment. Only pure anatomists, however, entertain this 

 last view and call this supposed segment the " microthorax," for 

 embryologists have not yet reported a metamere between the labial 

 segment and the prothoracic segment. Most embryologists who have 

 studied the subject admit that some of the cervical sclerites may be 

 formed from the last embryonic head somite which carries the labium 

 and probably forms a part of the back of the head. Therefore, if 

 it is desirable to retain the word microthorax as a name for a true 

 segment, it can be applied only to this labial metamere." 



The thorax, as has already been stated, is a distinct anatomical 

 region of the body rather than a " division " of tlie body, since it car- 

 ries both the legs and the wings and contains the large muscles for 

 each. Since the prothorax does not possess wings, it is not so highly 

 developed otherwise as the two wing-bearing segments, and is, indeed, 

 generally reduced in some ways, some of its parts being frequently 

 rudimentary. Therefore we shall base the following description of 

 a typical segment on the structure of the wing-bearing segments. 



A typical thoracic segment, then, presents four surfaces, as does also 

 the entire body. These are a dorsum above, a renter below, and a 

 latus ^ on each side. From these names we have the terms " dorsal," 



•^In a former paper on the thorax of insects (Proc. IT. S. Nat. Mns., XXXVI, 

 1909, pp. 511-595) the writer probably drew a too definite conclnsion on the 

 subject of the "microthorax." The origin of the neclc sclerites has i)robal)ly 

 never yet been actually observed. Comstock and Kochi (Amer. Nat.. XXXVI, 

 1902, pp. 13-^5), in summarizing the segmentation of the head, accredited 

 the gular and cervical sclerites to the labial segment, but did not recognize the 

 latter as taking part in the formation of the true head capsule. Riley, how- 

 ever, in his study of the development of the head of a cockroach (Amer. Nat., 

 XXXVIII, 1904, i)p. 777-810), states that in BUiitu the labial segment does 

 form a part of the back of the head and that the posterior arms of the 

 tentorium are derived from it. Burner (Zool. Anz., XXVI, 190:>. pp. 290-;>15) 

 and Crampton (Proc. Acad. Nat. Sci. Phila., 1909. pp. .S-54) believe that the 

 cervical sclerites are derived principally from the prothoracic segment. The 

 notion that they constitute a separate segment, the " microthorax," equivalent 

 to the maxilliped segment of the centipedes, has li(>;>n elaborated principally 

 by Verhoeff in his numerous writings on the Chilopoda and Derniaptera. 



* The writer introduces this word here because he knows of no other term 

 applied to the side of the segment in this sense. 



