444 SUMMARY OF CURRENT RESEARCHES RELATING TO 



heteromorplioses (tail in place of head and trunk), for the tail-like 

 appendage is to be considered as an imperfectly regenerated trunk, ft* 



The position of the reversed tail-stump with respect to the rest of 

 the organism is of importance during regeneration only in so far as it 

 influences the degree of efficiency of the structure regenerated. Neither 

 the present nor other experiments indicate that the influence of the 

 organism as a whole upon the regenerating part is able to bring forth a 

 heteromorphic structure, functionally adapted out of material which 

 would produce something else. 



In combinations between embryos of two species, each component 

 maintains its specific individuality. The modifications which may arise 

 in either of the components are not of the nature of a blending of specific 

 characters. In combinations where the tail alone is replaced by a tail 

 of the other species, the latter forms at first a perfect substitute for the 

 original tail. But later on it atrophies and disappears almost entirely, 

 long before metamorphosis. When a small portion of the trunk is 

 transplanted along with the tail, atrophy of the latter is considerably 

 delayed. Also when the two components are united in the region of 

 the pronephros, the composite larva grows normally, and may remain 

 healthy and vigorous for many weeks. Only in one case, however, did 

 such a specimen complete its metamorphosis. The frog had perfectly 

 normal instincts and power of co-ordination. The portions derived from 

 each of the two species could nevertheless be distinguished clearly by 

 their colour-markings and other specific characters. 



Variations in the Position of the Chick Embryo.*— Dr. Ch. Fere 

 remarks on the frequency with which the embryo of the chick may vary 

 in orientation. This may occur without known reason, and it tends to 

 increase the likelihood of other abnormalities. In many cases, however, 

 the anomaly of orientation is apparently unassociated with any other 

 abnormalities. 



Development of Bdellostoma Stouti.f — Dr. Bashford Dean gives a 

 general account of the development of this Myxinoid from the egg to the 

 time of hatching. After describing the spawning in Bdellostoma, he 

 discusses the question of protandrous hermaphroditism in Myxine, 

 which he holds to be unproved. The ovum of Bdellostoma is then 

 described, and the mode of development outlined. Then follow descrip- 

 tions of fertilisation, segmentation, the blastula, the gastrula, the early 

 and later embryos, and the newly hatched young. There are special 

 notes on integument, teeth, skeleton, nervous system, and viscera, &c. 

 Then follow general conclusions. 



The striking dissimilarity in the plan of development of Hyperotretes 

 and Hyperoartes points to a division of the Cyclostome phylum. The 

 few and yolk-filled eggs of Myxinoids contrast strongly with the many 

 and holoblastic eggs of the lampreys. 



The plan of gastrulation in Bdellostoma is highly specialised ; the 

 great bulk of yolk has played the usual part in modifying the mode of 

 appearance and the physiological relations of the embryo ; the origin of 

 the periblast-like nutritive layer parallels in an interesting way the con- 



* Journ. Anat. Physiol., xxxvi. (1900) pp. 210-6. 



t Festschrift C. von Kuppfor, Jena, 1899, pp. 221-76 (12 pis. and 25 figs.). 



