410 BUMMARY OF CURBENT RESEARCHES BBLATINa TO 



gradually grow toward the ventral side. Half-a-dozen or more of 

 these are specially modified as muscle-cells which serve to draw the 

 embryo into the shell. Another group extends forward and ventrally, 

 surrounding the oesophagus and the probable auditory sacs. A 

 few arrange themselves around the inner wall of the velum, and others 

 connect these with the cells round the oesophagus. Some are also 

 always found in the spaces between the outer walls and the mesenteron, 

 probably forming blood-corpuscles. The primitive mesoderm-cells 

 persist as late as the twentieth hour. The invagination of the shell- 

 gland, and the formation of the nautiloid shell are then described, 

 as also the changes in the foot, the appearance of the auditory organs, 

 and further progress which it is impossible to summarize. Owing to 

 the rapid abnormal development of the embryos, Dr. Patten has not 

 yet been able to contribute any definite results as to the development 

 of the nervous system. 



Development of the reproductive elements in Pulmonata.* — 

 Herr G. Platner continues his researches on the development of the 

 reproductive elements in Pulmonates. He has been able to watch 

 the process of copulation in confined Arions, and to trace the stages 

 in the maturation and fertilization of the ova. In Helix, even when 

 copulation had been observed, atrophy always set in, and the ova 

 never reached maturity. 



1. Karyokinesis in the sperm-cells of Helix. — To what he has pre- 

 viously communicated on this subject, Herr Platner adds the follow- 

 ing account of the origin and fate of the spindle-fibres. When the 

 chromatin of the regular coil is about to concentrate itself in the 

 granular equatorial plate, the spindle-fibres are seen neither meeting 

 at the poles, nor pursuing a straight course, but extending from the 

 equator towards the poles, and instead of ending sharply, bending 

 round to be continued on the other side. The spindle-fibres are 

 really the persistent framework of the regular coil, the chromatin 

 of which has been concentrated at the equator, while the unstained 

 ground-substance persists in toto. It seems probable that the micro- 

 Bomata are not solid, but disposed on the framework of the coil like 

 pearls on a string. The spindle is formed from the coil framework 

 by the concurrence of the individual segments of the latter in one 

 point at the poles, thereby becoming more stretched and entering 

 into intimate connection with the protoplasmic masses. In the usual 

 rapid division, the spindle-fibres seem suddenly to disappear, but 

 when division is slow their history can be traced. The pole-plates 

 separate from the spindle-fibres, fall into granules, and become 

 regular nuclei; the spindle-fibres contract more and more towards 

 the equator, fuse together, and form triangular or hook-shaped 

 structures, attached by their apex to the equator. After division 

 this structure retires from the periphery towards the centre ; the 

 limbs of the hook become longer and more distinct, diverging towards 

 the centre and then bending in and finally meeting. The closed 

 figure thus formed from the spindle-fibres is the accessory nuclear 



* Arch. f. Mikr. Anat., xxvi. (1886) pp. 599-621 (2 pis.). 



