196 



the skin of the Ammocoete. Her woodcut and plate, by the way, do 

 not tally with regard to the position of the anterior ventral series, 

 but this is doubtless due either to some such variation as is described 

 on p. 145, or to the fact that the drawings do not represent the same 

 stages. It would be interesting to learn whether there is any develop- 

 mental (relative) shifting of the sense organs like that seen in other 

 Fishes. These pits Miss Alcock immediately concludes are homologous 

 with the lateral sense organs of other Fishes — for what reasons we 

 are not informed. Now there are two totally distinct series of sense 

 organs found in the skin of Fishes — sense organs distinct both in 

 their histological structure and in their innervation. The one set, the 

 terminal buds or Endknospen of Merkel, is innervated by the cra- 

 nial nerves sensu stricto (e. g. the Vth, Vllth, IXth, Xth with 

 sometimes the spinal nerves), and the other set, the lateral line organs 

 (whether they be pit-organs, ampullary organs or canal organs) is inner- 

 vated by the series of lateral line nerves. The former also exist on 

 the visceral surfaces, when they seem to be innervated by a distinct 

 set of fibres (fasciculus communis), but the innervation of these somatic 

 and visceral buds still requires much elucidation. Now both these 

 series of cutaneous sense organs often exist side by side, as for ex- 

 ample they do in the Cod-fish, and it is necessary that the observer 

 should carefully distinguish between them. Whether Miss Alcock was 

 aware of the existence of two series of cutaneous sense organs in 

 Fishes I do not know, but we are given absolutely no reason for 

 believing that the sense organs she describes are true lateral sense 

 organs, and the description is, therefore, to put it mildly, imperfect. 

 I shall show later on that there is some reason for believing that her 

 "lateral line sense organs" belong to the other category. Dr. Gaskell 

 himself, I notice, is more cautious on the point. He says that the 

 lateral line organs in the Ammocoete "appear" to be represented by 

 the simple epidermal pits described by Miss Alcock. Before it can 

 be determined what these pits are they will have to be traced to the 

 adult form and examined histologically in the latter. The ventral line 

 from the IXth backwards is not represented in other recent or fossil 

 Fishes, and I should be greatly surprised to find that they were true 

 lateral line organs. 



On p. 135 the nerve referred to as the "ramus ophthalmicus 

 superficialis" has been wrongly identified. Assuming that the organs 

 it supplies are true lateral organs, the nerve will be the ramus buc- 

 calis facialis. Speaking from memory, the sense organs it supplies are, 

 according to Leydig, topographically infra-orbital in the adult, whilst 



