INTERNATIONAL ZOOUXJICAL CONGRESS. 246 



a muscle with its insertion belongs entirely to one and the same 

 segment, he proceeded to examine the musculature of the head. He 

 found that all the internal organs of the head, as seen in transverse 

 section, fall into easily recognised groups. The upper portion is 

 formed by the " proto-cerebral " segment, while the lower part is 

 derived, for the most part, from the mandibular segment. But within 

 this lower portion are to be found the derivatives of the maxillary 

 segment, which again enclose organs developed from the labial 

 segment. 



Dr. Heymons said that M. Janet's conclusion, based principally 

 upon a very careful study of the muscular system of the imago, that 

 the insect head is derived from six segments, one pre-oral, five post- 

 oral, is quite in accord with the results obtained by those who have 

 studied the embryology and the segmentation of the nervous system 

 in insects. Compared with this main point, the differences in matters 

 of detail which are necessarily the result of approaching the prol)lem 

 by ditlerent methods, are quite unimportant. It should be remembered 

 that even in the embryo, the boundaries of the mesoderm somites do 

 not precisely agree with those of the ectoderm segments to which they 

 belong, the somites always encroaching to some extent on the following 

 segments. As the muscular system arises from the mesoderm somites, 

 it is easy to understand that the insertions of the muscles in the imago 

 cannot always quite agree with the boundaries of the segmental plates 

 of the skeleton originating in the ectoderm. A thorough comprehen- 

 sion of the structure of the insect head must be attained by a careful 

 comparison of all the facts given by embryological and morphological 

 study, and it is not safe to carry too far the deductions to which one 

 particular series of facts would seem to point. 



Dr. Sharp considered that M. .Janet had advanced a most able and 

 brilliant hypothesis as to the relations of the complex structures of the 

 imago to the simple structures of the embryo, but it would remain for 

 the study of metamorphosis to corroborate or to contradict the details 

 of the supposed homologies. 



Classification of insects. — Dr. Sharp read a short paper giving a 

 now classification of insects. He pointed out that there were ditlfi- 

 culties in the arrangement by metamorphosis dividing them into 

 those having complete, incomplete and no metamorphosis, and pro- 

 posed a division into h'-rnjitcri/i/ota and Kiuh>jiU'nj(j(ita, or those having 

 the wings during tlie earlier stages as external buds, and those 

 having them as internal imaginal discs, adding Aptrri/t/ota for wingless 

 insects [Tlti/sanura find < 'ollcmbola) and Anautciijijiita for forms wing- 

 less, probably from loss of wings once possessed. Dr. Sharp's selec- 

 tion of this wing character is probably a very satisfactory one, but 

 we do not quite agree that the classification is a new one. The 

 division is still into Mrtabola and Anit-tahida ; but this wing character 

 is probably a much better one for distinctly and properly separating 

 these than those usually noted. In only one minor point does Dr. 

 Sharp appear to us to be in error, and that is in a suggestion that the 

 A}itiii/i/(ita [Collciiihola, etc.) may be transition forms between the 

 KxnpUrijijota and the Knd(<plciii<i(ita. The characters in which the 

 two latter agree together antl differ from the former, are too numerous 

 and important to make this possible, whilst a redevelojiment of 

 wings after an absence as complete as in Tlii/sanura would have been 



