Observations on the Torpedo, with an account of some additional experiments on its electricity

Abstract

The first part of this paper is occupied by an investigation of the circumstances attending the fœtal development of the Torpedo. In the first stage of embryonic growth which the author had an oppor­tunity of observing, when the embryo was about seven tenths of an inch in length, it had neither fins nor electrical organs, nor any ap­pearance of eyes; it exhibited short external branchial filaments, not yet carrying red blood; and there was a red spot in the situation of the heart, communicating by red vessels in the umbilical cord with the vascular part of the egg. There is no membrane investing the fœtus, as is the case with some species of Squall ; nor any fluid in the uterine cavity; neither could the author find any urea or Iithic acid in that cavity. By taking the mean of many observations, it appeared that the weight of the egg, before any appearance of the embryo, is 182 grs., and after its appearance, including the weight of the latter, 177 grs.; while the weight of the mature fish is about 479 grs.; showing an augmentation of more than double. Thus it differs remarkably, in this respect, from the fœtal chick, which at its full time weighs consider­ably less than the original yolk and white from which it is formed. No communication can be traced between the fœtus of the Torpedo and the parent, through the medium of any vascular or celiular structure; and the stomach of the former is always found empty. Hence the only apparent source of nourishment is absorption from the surface; and the author states his reasons for believing that the branchial fila­ments are the principal absorbing organs, the materials they receive being chiefly employed in the construction of the electrical organs, while those which enter into the composition of the body generally are absorbed by the general surface of the fœtus. The author is led, from his researches, to the conclusion that the mode of reproduction in the Torpedo is intermediate between the viviparous and the ovoviviparous. In the second part of the paper, the author discusses the question as to the number of species of the genus Torpedo existing in the Mediterranean; and concludes that there are only two, viz. the Ochiatella and the Tremola .