304 SUMMARY OF CURRENT RESEARCHES RELATING TO 



As to the origin of the musculature of the anterior extremity, he 

 finds that myotomes 9-13 give off ventral prolongations which do not 

 directly give rise to the muscles, as Mollier supposes, hut which con- 

 stitute the primordium of the ventral musculature, from which secondarily 

 muscle-cells pass out to the extremity. The hypoglossus muscles arise 

 from the ventral prolongations of myotomes 2— 5, the first myotome heing 

 rudimentary. The oculomotor muscles arise from the wall of the head- 

 cavity, which developes in an embryo with one to two primitive segments 

 from the entoderm at the anterior end of the chorda. The primordia 

 originate from the epithelial wall of the cavity, and then separate from 

 it, growing towards the bulbus, and towards their later origin and 

 insertion. The M. rectus extemus arises from a cell-mass, the epithe- 

 lial origin of the elements of which points to a derivation from a head- 

 cavity. The M. obliquus superior originates from the dorsal part of 

 the trigeminus muscle primordium. Of the muscles of the gill-arches, the 

 trigeminus and facialis only were investigated. They arise from the 

 proliferation of the medial plate of the coelom spaces, after these have 

 been separated by the appearances of the gill-slits, and are of distinctly 

 splanchnic origin. 



Giant Spermatids in Bombinator igneus.* — Dr. Ivar Bromar de- 

 scribes giant spermatids constantly present at the reproductive period. 

 They are usually multinucleate, and in the midst of the nuclei there lies 

 a sphere or an idiosome, with numerous centrosomes. One nucleus is 

 usually much larger than the rest, and all are connected by processes 

 with the central idiosome. The giant spermatids seem to arise by 

 pluripolar mitoses from giant spermatocytes of the second order, and 

 the transformation is discussed in detail. Many of the giant spermatids 

 degenerate ; others form giant or monstrous spermatozoa. 



Spermatozoa of Bombinator igneus.f — Dr. Ivar Bromar has in- 

 vestigated the structure and development of the remarkable sperms of 

 this toad. As to structure, each has a greatly elongated head with a 

 central supporting rod, and two central corpuscles at its anterior end. 

 To the posterior of these the tail is attached. It consists of two 

 filaments, a slender motile one and a thicker supporting one which is 

 not actively motile. The former is furnished with a delicate mem- 

 branous fringe (fin-membrane), and is longer than the latter, with which 

 it unites in the vicinity of the posterior end of the head. As to develop- 

 ment, after the second maturation division the two central corpuscles 

 are to be seen, surrounded by the idiosome, arranged in a line perpen- 

 dicular to the cell-margin. While the two spermatids are still connected 

 by the remains of the spindle, the central corpuscle nearest the periphery 

 begins to grow out into a filament which is the first beginning of the 

 motile thread of the tail. As it grows, the idiosome with its contained 

 corpuscles moves inwards towards the nucleus, dragging the thread 

 with it, and a vesicle appears at the side of the idiosome, which increases 

 as the idiosome itself diminishes. As idiosome-vesicle, idiosome, and 

 central corpuscles reach the nucleus, this rotates about its middle point 

 through a half-circle, the ultimate result being that when the head is 



* Anat. Anzeig., xvii. (1900) pp. 20-30 (10 figs.). 

 t Tom. cit. pp. 129-45 (24 tigs.). 



