69 



in Lamellibranchiates when they are placed in their normal 

 position for comparison. He then showed that this is not 

 objectionable when we take into account such forms as Cla- 

 vagella and similar Lamellibranchiates, and that we have the 

 same symmetry between the two halves of the anterior and 

 posterior valves which we find between the right and left 

 valves of the Lamellibranchiates, From this it would follow 

 that the foot of the Lamellibranchiates is homologous to the 

 stem of a Bryozoon. 



Mr. Scudder made some remarks upon tlie division of the class of 

 Insects Into orders, and its relations to other members of the branch 

 of Articulates, on considerations drawn from the external integu- 

 ment of the animal. He showed that the different modes in which 

 the plan of articulation is carried out are exhibited in Insects by a 

 grouping together of the segments of which the body is composed 

 into three distinct regions ; in Crustacea, by a similar grouping, into 

 two regions ; while the worms show no regional distinction whatever. 

 If a "region" be defined (among Articulates) as such a definite asso- 

 ciation of segments, in a more intimate relationship to one another 

 than they exhibit towards other segments or association of segments, 

 as is indicated more or less in the general contour of the body, and 

 when accompanied by appendages, these applied to some special pur- 

 pose, — then the so-called cephalothorax of Arachnids is, in reality, 

 composed of two distinct regions, with the dorsal portions of the seg- 

 ments composing them, so closely united iato a pseudo-cephalotho- 

 racic shield as to have caused them to have been generally consid- 

 ered as forming but a single region ; while in the segments of the 

 Myriapod, which bear no genuine legs, we have a more true cepha- 

 lothorax than in the soldered front-body of the Arachnid, while, at 

 the same time, there is in the Myriapod a front portion clearly sepa- 

 rated from and freely movable upon the hind portion, the one homol- 

 ogous with the head of the Hexapod, and the cephalic portion of the 

 pseudo-cephalothorax of the Arachnid ; the other with the thorax of 

 the Hexapod, and the thoracic portion of the pseudo-cephalothorax 

 of the Arachnid. In the varied intimacy of the relationship existing 

 between these three regions of the body, and the development of the 

 segments composing them, we have three different degrees of compli- 

 cation of the Insect-structure, forming thus three natural orders: 

 Hexapoda, Arachnida, and Myriapoda. 



Mr. Putnam referred to the statements made by him at a previous 

 meeting, in regard to the striped and spotted snakes, Coluber ordinatus 

 and sirtalis of Linnaeus, and said that he had this day received a let- 



