934 



SCIENCE 



[N. S. Vol. XXIX. No. 754 



and lie controls the statements of the book by 

 his observations in the laboratory; and where 

 the latter are incomplete they can be supple- 

 mented by reference to the former. 



The continued usefulness of this little book 

 is an object lesson in embryological pedagogy 

 by which the writer tried to profit in writing 

 a new "Development of the Chick" which 

 should bring the subject matter up to date, 

 and serve as an introduction to embryology. 

 On the whole it seems improbable that the 

 chick will be displaced as the favorite subject 

 for laboratory practise in embryology, because 

 the material is of universal occurrence and 

 available at all seasons of the year without 

 great expense. Moreover, the technique is as 

 simple as that of any other form, at least after 

 the egg is laid; and the knowledge of its 

 development, while yet incomplete, is certainly 

 more considerable than that of any other ani- 

 mal with the possible exception of man him- 

 self. 



Professor Metcalf's objections to the use of 

 the chick for introducing students to the sub- 

 ject of embryology' do not appear to me to be 

 well grounded. He complains that the embryo 

 chick is "highly specialized" and "distorted 

 from the general vertebrate type," and that 

 "the space relations of the organs are dis- 

 torted by secondary influences." Tor these 

 reasons he prefers the frog, and wishes that 

 there were an embryology of this form. I 

 echo this wish and hope that Professor Met- 

 calf will undertake to write one. I am afraid, 

 however, that the inconsiderate agricultural- 

 ists who domesticated the hen and taught her 

 to lay the year around have conferred on her 

 an unfair advantage; and it appears to me 

 better for the elementary student to study 

 living hens' eggs than preserved frogs' eggs. 

 This is indeed the main advantage that I see 

 on the side of the chick. But I believe that 

 the objections on account of " specialization " 

 and " distortion " are more deeply rooted in 

 tradition than in nature. 



But whether the student uses the frog or 

 the chick, or some other form, he needs a 



' Science, N. S., XXIX., May 7, 1909, pp. 738- 

 739. 



fairly complete and modern book of reference 

 of the same form, if not to replace, at least to 

 supplement, the comparative text-books. In 

 this contention I think Professor Metcalf will 

 agree. "We need above all objectivity in the 

 teaching of embryology; we must require some 

 basis of exact facts to support generalizations, 

 and keep the distinction between the two clear 

 in the student's mind. 



Frank E. Lillie 

 Univebsity of Chicago 



genera without species 

 In Science for February 26, 1909 (pp. 339, 

 340), Professor Cockerell discussed the "con- 

 troversy " concerning " genera without spe- 

 cies," pointing out the difficulty of dealing 

 with such cases, since they are not distinctly 

 provided for in the International Code of 

 Zoological Nomenclature. Apparently each 

 case should be dealt with solely on its merits. 

 A few illustrations may help to make this 

 point clear. In 1799 Lacepede proposed the 

 genus Picoides, giving a short diagnosis of it, 

 but omitting to refer to it any species. The 

 diagnosis clearly indicates a woodpecker hav- 

 ing only three toes. The only species of wood- 

 pecker at that time known with only three toes 

 was the three-toed woodpecker of northern 

 Europe, Picus tridactylus Linn. This species 

 being clearly the basis of the diagnosis, it may 

 be taken as the type of the genus Picoides, 

 now, for a long time, current for the group 

 containing this and other closely allied species. 

 In the same way, and at the same date, 

 Lacepede proposed the name Astur for a 

 genus of short-winged, long-legged hawks, 

 giving for the genus a wholly inadequate diag- 

 nosis, without mentioning under it any 

 species. In 1806 Froriep published a Ger- 

 man translation (" Analytische Zoologie ") 

 of Dumeril's " Zoologie analytique," adding to 

 it, passim, much new matter, including the 

 mention of examples under Dumeril's genera, 

 which, for the most part, were originally pro- 

 posed by earlier authors, without, of course, 

 the designation of types. As an example of 

 Astur Froriep gave the species Falco palum- 

 harius Linn., which thus may be taken as the 

 type of Astur. But the genus should date 



