46 



batis). He has, however, studied the two dog-fishes 

 fScylliuni caniciila and Pristiiinis jjiehinnstomn), the spiny 

 dog-fish (AcnntJiias vulgaris), the torpedo fish (Torpedo 

 ocellnt(i), the chick, etc., etc. His work on Pristiurus is 

 ready for the press. 



For the past twenty years Beard has heen a most 

 energetic student of the structure and development of the 

 Elasmobranch fishes. He may thus elaim to write with an 

 authority derived from actual first-hand knowledge. As 

 already stated, Beard commenced his researches with a view 

 of determining by observation the " apparently simple question 

 " of the mode of development of a vertebrate animal." His 

 object was to trace the entire course of development, from 

 the egg of one generation to the egg of the following 

 generation. This had never previously been done. Its 

 accomplishment would solve many outstanding problems, 

 and, as the sequel proves, many unforseen results have been 

 attained. It must be particularly noted that Beard worked 

 for years holding the generally accepted view of direct 

 development. We have already noted the text book teaching 

 on this, that eggs give rise to embryos which are but phases 

 in the development of the individuals, that the individuals 

 give rise to germ -cells, and so on. 



The study — by Beard — of serial sections of a very large 

 number of embryonic skates revealed the fact that germ-cells 

 were not confined to the germinal ridge alone, but were to be 

 met with in almost every organ of the body, " Sometimes they 

 " may be found in the head, head-somites, brain, the gill-region, 

 " the skin of the trunk or head, the pericardium, the liver, even 

 " occasionally in the blood, the kidney-tubules, the body-cavity, 

 " myotomes, spinal-cord, gut-epithelium, especially of the yolk- 

 " stalk and of the rectum, etc., etc. — in fine, there is hardly a 

 " place in the whole trunk or head in which such aberrant 

 " germ-cells have not been observed."* If then these abnormally 

 placed germ-cells are the products of the peritoneal epithelium 

 they have evidently migrated from their place of origin ; they 



♦ John Beard, Morph. Con. Rev. Neiii: and Psych., Jan., 1904 : p. 19 " 



