Abstract
There are, in relation to the number of ganglia, three main types of ventral nerve cords in the adult stingless bees: 1) Those which have two ganglia in the thorax and five in the abdomen, 2) those which have two ganglia in the thorax and four in the abdomen, and 3) those which have three ganglia in the thorax and four in the abdomen. Intermediate types between those listed exist.The most generalized ventral nerve card was found in the workers of Trigona fulviventris, where each ganglion lies only one segment ahead from its respective segment (Fig. 1, A). When this generalized type of nerve cord is taken as a starting point, there are two major recognizable evolutionary trends almong the stingless bees (Fig. 1). One trend is toward the fusion of ganglion 7 with the preceding abdominal ganglion. This occurs independently in the several subgenera of Trigona, with a series of intermediate steps (Fig. 3, A to H). Among some of the species of Melipona there is also a tendency of fusion of ganglion 7 with ganglion 6 (Fig. 4, A to D ) but none of the species of Mélipona dissected was found with those ganglia completely fused.The second trend noted is toward cephalization of the nerve cord ( Fig. 2). This occurs only in Melipona. Here the abdominal ganglia migrate from two to four segments ahead from their respective segments. As a result, ganglion 3, which in primitive forms was located in the second abdominal segment (first metasomal segment), has moved well inside the thorax. The presence of ganglion 3 in the thorax is characteristic of all the species of Melipona. The highest type of cephalization is found only in a few species, such as MeliPona flavipennis in which ganglia 4 and 5 have moved into the second abdominal segment, and ganglia 6 and 7 into the third. Therefore, in this type, the card extends in the abdomen only as far as the third abdominal segment (second metasomal segment, Fig. 2, E ) . There are, of course, intermediate types.
Highlights
most generalized ventral nerve card was found in tbe workers of Trigona julviventris
When this generalized type of nerve cord is taken as a starting point
One trend is toward the fusion of ganglion 7
Summary
A p,ilper (WILLE, 3 ) dealing with the dorsal vessels of bees, published as a result of a preliminary study on the relationships of the genera and sub· genera of the Meliponini, led to a comparative study among other bees. The present paper is a continuation of the same type of work, dealing with the ventral nerve cord. Since other investigators are working with the nervous system of the bees, the present work deals only , with the Meliponini, reference to other bees is made when necessary. Subgenus PLEBEIA : Trigolla beeearii Gribodo, Trigolla .assiae Cockerell, Trigolla denoiti Vachal, Trigona em erina Friese, Trigona 1'(:. Subgenus PARATRIGONA : Trigona sub· Iluda Moure. Subgenus PAR· TAMONA : Trigocm cupira Smith, TrigOJ1C1 testaeea 17lusarmn Cockerell. SUDgenus HYPOTRIGONA : Trigona braunsi Kohl, T1'igona buyssoni Friese, Trigona duekei Subgenus OXYTRIGONA : Trigona tataira méllicolor Packard. Subgenus CEPHALOTRIGONA : Trigona capitata zexmeniae Cockerell. Dissections were done under water, aad several specimens were dis sected for every species examined. 1 is that of the propodeum (first abdominal segment ) ; 2, of the first metasomal segment (second abdominal segment) , etc
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