MORPHOLOGY OF BRAIN AND SENSE ORGANS OP LIMULUS. 33 



different function^ can be followed in great detail, and furnishes 

 a most remarkable instance of change of function and structure. 

 A fact, however, of great morphological significance is the 

 striking resemblance between the structure and mode of 

 development of the olfactory organ in Limulus and that of 

 the so-called ''frontal Sinnesorgan'' of Phyllopods, as de- 

 scribed by Leydig, Glaus, and others. Clauses description 

 of this organ in Branchipus will serve equally well for Limulus. 

 The peculiar " kolbenformige" cells described by him as 

 originating from the brain ; their position beneath the ecto- 

 derm in ommatidia-like clusters, and containing the refractive 

 "zinkage" needles; their position in relation to the median 

 eye, as well as their relatively late appearance, are much the 

 same as in Limulus. It seems to me there can be but little 

 doubt that the frontal organ of Branchipus, with its ganglion- 

 cell masses arising from the median part of the brain, corre- 

 sponds to the median nerve and median olfactory region of 

 Limulus; while the " Kolbenzellen" organ, with its lateral 

 ganglionic nerves, corresponds to the lateral nerve and primi- 

 tive sense organs of Limulus. Of course at first sight the 

 appearance of the organ in Limulus is different from that in 

 Branchipus, but its fundamental structure and relations to the 

 brain are the same. These facts point conclusively to a much 

 closer genetic relationship between Limulus and the Phyllo- 

 pods than has been recently supposed to exist, and this sup- 

 position has further support in the similarity in the develop- 

 ment of the trifold median eyes. If a more careful compara- 

 tive study of the frontal organ in other Phyllopods — Apus, 

 for example — should confirm the above comparison, it would 

 settle once for all the vexed question of the relation of 

 Limulus to the Crustacea, and would furnish very strong 

 evidence of the common ancestry of Crustacea and the Arach- 

 nids in the trilobites. 



III. The Gustatory Buds of the Mandibles. 

 It will be remembered that our physiological experiments 



vol. 35, PART I. — NEW SKR. C 



