OcTor.KK 8, 1896J 



NA TURE 



561 



Upon comparing this organ with the olfactory organ of Ammo- 

 cretes we see a most striking resemblance in general arrangement 

 and structure. 



Just as the mouth tube of Tholyphnnus is formed of two 

 parts, the pedipalp and camerostome, so, according to Kuppfer, 

 the nasal tulic of Ammoccetes is composed of two parts, the 

 upper lip and the olfactor)- protuberance. Of these two parts 

 we see that the upper lip, or hood, like the pedipalp, is inner- 

 vated by the Vth nerv-e, or nerve of the jirosomatic appendages, 

 while the olfactory protuberance, like the camerostome, is inner- 

 vated by the 1st nerve. Kupjifcr's investigations show us 

 further (Fig. 9) how the olfactory protuberance is at first free, is 

 <lirected ventralwards, and lies at the opening of the hypophysial 

 tube ; how afterwards, by the forward and upward growth of 

 the upper lip to form the hood, the nasal tube is formed with the 

 result thai tlie nasal opening lies on the dorsal surface jusi in 



^m/tiAaiSi0'iiffy 



'irli/i orJhliza -^fsttmo' 





Fig. 9.--A, m<:dian sagittal section through head of young Thelyphonus ; 

 B, ditto, yuuHR Aminoco^te (after Kuppfer) ; c, ditto, full-grown 

 AmmcC'L'le (after Kuppfer). 



front of the pineal eye. Kuppfer, like Dohrn and Beard, looks 

 upon thishypophysial tube as indicating the imteostoma, or original 

 mouth of the vertebrate, a view which harmonises absolutely 

 with my theory, and receives the simiilest of explanations from 

 it, for, as you .see on the screen, sections through the mouth tube 

 of Thelyjihonus correspond absolutely with sections through 

 the nasal tube of Ammoccetes ; here in the one section is the 

 projecting camerostome, there is the corresponding projection of 

 the olfactory protuberance, here is the sense-epithelium of the 

 lower lip or hypostoma, there is the sense-epithelium of the 

 upper lip or hood. Here, as Fig. 9 shows, the mouth tube 

 passes in the ventral middle line to where it turns dorsalwards 

 into the miiUlle of the conjoined nervous mass of the supra- and 

 infra-resopbageal ganglia. There the nasal tube ends blindly at 

 the spot where the infundibular tube lies on the surface of the 

 brain. 



Further, the topography of corresponding parts is absolutely 



NO 1406, VOL. 54] 



the same in the two animals : in the dorsal middle line the 

 rostrum, with the two median eyes near its extremity ; in the 

 corresponding position the two pineal eyes ; below this, in the 

 middle line, the camerostome ; corresponding to it in the Am- 

 mocoetes the olfactory protuberance ; then the modification of 

 the median projections of the foremost ventral appendages — the 

 pedipalpi — to form the hypostoina in the corresponding position 

 the upper tip or hood of Ammoccetes, which forms the hypo- 

 stoma as far as the hypophysial tube or palreostoma is concerned, 

 but an upper lip as far as the new mouth is concerned. The 

 muscles of this upper lip belong all to the splanchnic and not to 

 the somatic group, and are innervated by the appropriate nerve 

 o( the prosomatic appendages, viz. the motor part of the Vth. 

 Ventral to the pedipalpi in Thelyphonus there is nothing, 

 ventral to the corresponding lip in the Ammoccetes is the lower 

 lip, and we have seen that, although such a structure is absent 

 in the -land scorpions of the present day, it was present in 

 the sea scorpions of old time, was known as the metastoma, and 

 is supposed to be a forward growth which started at the junction 

 of the prosoma with the mesosoma. Precisely corresponding to 

 this we see from Kuppfer that the lower lip of Ammoccetes is a 

 forward growth from the junction of the slomatodreum with the 

 respiratory chamber. 



We see then, so far, that the comparison of the vertebrate 

 nervous system with the conjoined central nervous system and 

 alimentary canal of the arthropod has led to a perfectly con- 

 sistent explanation of almost all the peculiarities of the head 

 region of .\mmoccetes. We have solved the segmentation of 

 the skull and the mysteries of the cranial nerves, for we have 

 found that the cranial segmentation of the vertebrate can be 

 reduced to the segmentation of the prosomatic and mesosomatic 

 regions of the Limulus, that the cranial skeleton arose from the 

 modified internal chitinous skeleton of the Limulus, that the 

 new mouth was formed by the forward growth of the metastoma, 

 leading to the formation of an oral chamber, while the old 

 mouth remained as the hypophysial tube, guarded by its olfac- 

 tory and taste organs. 



Search as we may in the prososomatic and mesosmatic regions 

 of scorpion-like animals, there are but few points left for elucida- 

 tion ; among these the most important are : ( i ) the fate of the 

 ccelomic cavities and coxal gland ; (2) the fate of the heart ; 

 (3) the fate of the external chitinous covering. 



Comparison of the Head Cavities of the Verlehrale with the 

 Prosom itic aud Mesosomatic Calomic Spaces of Limulus. 



A recent paper by Kishinouye (Joiirn. of Coll. of Sci. Tokio, 

 vol. v., 1891) on the development of Limulus enables us to com- 

 pare the ccelomic cavities in the head region of a vertebrate with 

 those of the prosomatic and mesosomatic segments of Limulus, 

 and we see that the comparison is wonderfully close ; for 

 whereas each mesosomatic segment possesses a ccelomic cavity, 

 just as each of the segments of the branchial chamber supplied 

 by the vagus, glossopharyngeal, and facial nerves possesses a 

 ccelomic cavity, this is not the case with the prosomatic seg- 

 ments. In these latter the first coelomic cavity is a large prteoral 

 one, common to the segment of the first appendage and all the 

 segments in front of it ; the segments belonging to the second, 

 third, and fourth appendages have no coilomic cavities formed 

 in them, the second ccelomic cavity belongs to the segment of 

 the fifth appendage. Similarly in the vertebrate in the region 

 corresponding to the prosoma there are only two head cavities 

 recognised, viz. the ist prxoral head cavity of Balfour and V. 

 Wijhe ; and 2nd or mandibular head cavity, associated especially 

 with the Vth nerve. According to my view the motor part of 

 the Vth nerve represents the locomotor prosomatic appendages 

 of Limulus, and we see that already in Limulus the three fore- 

 most of these appendages do not forin ccelomic cavities. 



In fact, the agreement in the formatirm and position of the 

 ccelomic cavities in the head region of the vertebrate and in the 

 prosomatic and mesosomatic regions of Linmlus could not well 

 be more exact ; further, these cavities agree in this, that in 

 neither case are they permanent ; both in the vertebrate and in 

 the arthropod they are supplanted by vascular spaces. 



Comparison of the Pituitary Gland with the Co.xal Gland oj 

 Limulus. 



In connection with the second ccelomic cavity in Limulus is 

 found an ancient gland, partially degenerated according to some 

 views, which was probably excretory in function, and has been 



