18 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Head of Embryo Chlamydoselachus.*— Paul Brohmer has studied 

 the cavities of the head and the nerves in this type. Two of his con- 

 clusions may be stated. Piatt's head-cavity is absent in some Selachians 

 {Chlamydoselachus and Torpedo) ; in the others it is comparable to the 

 diverticula which arise from the mandibular cavity, and are subsequently 

 constricted off. These have no significance in connection with the head 

 problem. The third head-somite of Van Wijhe is the upper portion of 

 £he hyoid cavity. In young embryonic stages the two form one cavity, 

 but the upper part is subsequently separated off and seems independent. 



Development of Heart in Teleosts.f — I. Borcea finds in Belone, 

 and other Teleostean fishes, that the heart and the migratory vascular 

 cells (which form the vitelline network), arise from part of the cephalic 

 mesoderm, corresponding to the intermediate mesodermic masses in the 

 trunk. On the other hand, the pigment-cells have an ectodermic origin. 



Intermediary Mesodermic Mass in Teleost Embryos.^ — I. Borcea 

 has studied, in various types {Belone, Exocatus, Gobius, etc.), the 

 intermediary differentiation of mesoderm which was first described by 

 Oellacher. He finds that it gives origin to the endothelium of the 

 blood vessels, the blood corpuscles, the renal canaliculi, and the lymphoid 

 tissue of the kidney. 



Development of Marsupial Skull. § — R. Broom gives an account 

 of his observations on the development of the skull in Trichosurus 

 vulpecula and Dasyurus viverrinus. We cannot do more than refer to 

 a few points. There is a remarkable resemblance between the skull of 

 the very young Echidna (as described by Gaupp), and that of the young 

 Dasyurus. " In fact, the Dasyure skull resembles that of Echidna more 

 than it does that of Trichosurus.' 1 '' 



The parachordals and trabecule are very definite structures, but the 

 occipital region is not very clearly differentiated from the parachordal. 

 The trabecular form all the median, basal cartilage in front of the 

 parachordals. The paraseptals are probably true parts of the nasal 

 capsule, the base of the latter being trabecular. A large lateral carti- 

 lage, which the author calls orbitosphenoid, seems to be as definitely 

 a cranial element as the trabecula. It is continued backwards, and fuses 

 with the auditory capsule, though quite distinct from it. There is 

 some reason to consider that the supra-occipital is the further continua- 

 tion of the same band. Broom argues in support of the rather startling 

 conclusion that the element which develops into the alisphenoid is a 

 specialisation of a rudiment of the palatopterygoid arch. 



Blood-formation in Embryonic Mammalian Liver. || — S. Mollier 

 finds that in embryos of man, cat, rabbit, etc., blood-cells are formed 

 in the liver from an indifferent material, the reticulum. This is due to 

 the visceral layer of the mesoderm, and differentiates into endothelium, 



* Jenaische Zeitschr. f. wiss. Nat., xliv. (1909) pp. 647-98 (4 pis. and 15 figs.), 

 t Cornptes Rendus, cxlix. (1909) pp. 688-9. J Tom. cit., pp. 637-40. 



§ Proc. Linn. Soc. N.S.W., xxxiv. (1909) pp. 195-214 (8 pis.). 

 || Arch. Mikr. Anat., lxxiv. (1909) pp. 474-524 (4 pis. and 8 figs.). 



