ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 977 



exhibited, and the looped chromatin filaments dispose themselves 

 parallel to the achromatin threads of the spindle and recede towards 

 the poles where some of them bend in a bow-shaped fashion. There 

 small spheroidal vesicles are formed from the chromatin, which is 

 not, however, spread regularly over their surface, but in minute ac- 

 cumulations here and there, the interspaces being probably occupied 

 by achromatin. These little vesicles unite and fuse to form the new- 

 nuclei, and the active protoplasm of the cell gathers round each in a 

 star-like form, round which again the pigment-granules are radiately 

 disposed. The active protoplasm thus collected colours readily on 

 being treated with Schweigger-Seidel's acid-carmine in chromo-acetic 

 acid preparations, the forming nuclear substance colours intensely, 

 the spindle only very slightly, so that Bellonci would infer some 

 chemical change of the nuclear substance during karyokinesis. 

 As the spindle is about to divide the pigment covers it, hiding and 

 then replacing the connecting filaments, across which a cellular plate 

 with an abundant deposit of pigment eventually appears. The 

 peculiarity of the process consists in the formation of the small 

 vesicles of chromatin, and probably also of achromatin, which unite 

 to form the two new nuclei, but this is only a slight modification of 

 the ordinary karyokinesis observed in the somatic cells. 



Epidermic Cells of Tadpoles.*— Dr. A. Kolliker has discovered 

 in the tail of young frog larvfe, numerous epidermic cells, each with 

 a stiff process projecting on the exterior ; the superficial flat cells of 

 the epidermis are so arranged as to leave a series of small boles, 

 through which the tips of these processes protrude. These cells 

 appear to be peculiar to the Anura, and were not found in any Urodeles ; 

 they are chiefly aggregated in the lateral line, but are found else- 

 where ; these cells are undoubtedly sensory and have been proved to 

 be connected with nerve-fibres. 



Early Developmental Stages of Torpedo.f — Dr. A. Swaen finds 

 that in Torpedo ocellata the mesoblast arises from the front end of the 

 embryo from a layer of cells termed the secondary hypoblast ; the 

 secondary hypoblast forms the upper wall of the archentei-ic cavity, 

 its lower wall consisting of the primitive hypoblast, which appears to 

 correspond to the " lower layer cells " of Balfour. The formation of the 

 chorda and of the mesoblast, derived as they are from the walls of the 

 archcnteron, is similar to the mode of formation of the same structures 

 in Amphioxus, except that they are not hollow, and are not therefore 

 precisely diverticula of the archenteron. 



Tlie first traces of the vascular system are to be found in the 

 peripheral portion of the extra embryonal zone ; they arise as 

 " blood-islets " in the cells of the hypoblast, but afterwards grow into 

 the mesoblast and become shut ofi" from all connection with the hypo- 

 blast ; the hypoblastic cells form the blood-corpuscles, but the walls 

 of the tubes are at least partly mesoblastic. 



The portion of the secondary hypoblast which remains over after 



* Zool. Anzeig., viii. (1885) pp. 439-41. 



t Bull. Acad. R. Sci. Bclg., ix. (188.'5) pp. 385-416 (16 figs.). 



