338 SUMMARY OF CURRENT RESEARCHES RELATING TO 



represents the extreme of rapid egg production, other forms of which are 

 found in the production of two eggs united by a membranous tune ; two 

 eggs at the same time ; two eggs at different times on the same day, 

 and a daily egg-production where the eggs are. laid earlier on each 

 successive day. The two yolks of a double-yolked egg may have all the 

 envelopes in common, or each may possess one or more separate 

 envelopes. All possible intermediate forms were found, indicating that 

 the two yolks may come together at any point between the mouth of 

 the funnel and the isthmus. Various disturbances of the normal pro- 

 cesses of egg production may bring two yolks together in the oviduct. 

 Double-yolked eggs evidently do not always represent simultaneous 

 ovulations. The double-yolked eggs contain more albumen and have a 

 heavier shell than single-yolked eggs, and in triple-yolked eggs these 

 parts are heavier still, but in neither case is the increase in direct pro- 

 portion to the increase in the weight of yolk. Multiple-yolked eg;gs 

 are longer in proportion to their breadth than the normal eggs of the 

 same individual. A series of tables showing the relation of multiple- 

 yolked eggs to the age of the bird is given, and the different stages of 

 union are illustrated by diagrams. 



Development of Columella auris in Chrysemys marginata.* — Lucy 

 W. Smith has made a study of the origin and development of the 

 columella auris in Chrysemys marginata. She finds that in an early 

 pre-cartilage stage the condensations of the skeletal elements (hyoid 

 cornu, interhyal, and columella auris) of the hyoid arch are continuous. 

 The columella auris represents the dorsal portion of the hyoid arch, and 

 originates as a single element. In the adult the columella proper 

 ossifies and closes the fenestra ovalis. The extra-columella always 

 remains in a cartilaginous condition. The interhyal represents, onto- 

 genetically, the upper extremity of the hyoid cornu. The tympanic 

 cavity is formed from the hyomandibular cleft. The columella has no 

 distinct ligamentous or muscular attachments of morphological value, 

 such as the ligamentum hyo-columellare, or mandibulo-hyoidale. 



Development of Lungs in Bombinator igneus.f — M. Makuschok 

 describes the early development of tbe lungs in this Amphibian, and 

 compares it in detail with that of the gill-pouches. Differing from 

 Greil, who has been over the same ground, Makuschok finds that the 

 facts support the view that lungs and gill-pouches are homologous. 



Development of Vascular System of Lamprey.} — W. Keiser has 

 proved for Petromyzon planeri the mesodermic origin of the heart, the 

 two main longitudinal vessels, and the first embryonic blood. The 

 endocardium is formed by the combination of a group of free mesen- 

 chyme cells into a loose tissue which gradually assumes a tubular form. 

 The endothelium of the vessels is likewise due to a combination of free 

 mesenchyme cells. There is thus a close resemblance between the 

 development of the vascular system in the lamprey and that in Dipnoi 

 and Amphibians. 



* Anat. Anzeig., xlvi. (1914) pp. 547-60 (9 figs.). 



t Anat. Anzeig., xlvi. (1914) pp. 293-309 (9 figs.). 



t Jen. Zeitschr. Naturw., li. (1914) pp. 579-626 (5 pis. and 30 figs.). 



