ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 51 



of other investigators. After describing the hermaphrodite glands 

 of Arion and Helix and their relation to the enveloping liver-mass, 

 he gives a detailed account of the different stages in the development 

 and differentiation of the sperms. 



(a) The spermatogonia are at an early stage the only cells in the 

 gland besides the ova. They possess little protoplasm, a large 

 slightly granular nucleus, a distinct nucleolus, but no enveloping 

 membrane. Each contains a peculiar body independent of the nucleus ; 

 in Arion, apparently consisting of a number of small rods forming 

 a more or less regular figure, in Helix in the form of a coiled filament. 

 The spermatogonia exhibit indirect division, and the peculiar rods or 

 coils are also doubled during the process, but when the spermatogonia 

 in ceasing to divide, have formed a mass of spermatocytes, the peculiar 

 bodies have finally disappeared. 



(6) The spermatocytes are smaller than the spermatogonia, have 

 not, as has been mentioned, that peculiar body, and their nuclei never 

 exhibit the quiescent condition, nor consequently a nucleolus. The 

 spermatocytes group themselves round basal cells, which ajjpear at 

 an early stage from the cells adjacent to the alveolar wall, and 

 resemble spermatogonia in form, though not in history. Their large 

 oval, granular nucleus, which does not divide, is surrounded by a 

 finely granular protoplasm. With these centres the spermatocytes 

 are directly associated. All spermatogonia, however, do not form 

 spermatocytes, a large proportion of them persist, arranged in pillars, 

 between the spermatocyte groups, and form subsequently, not only a 

 new generation of spermatocytes, but also new basal cells, after the 

 others have disappeared. 



(c) The spermatocytes divide indirectly to form spermatides or 

 undifferentiated spermatozoa. In both this division and that of the 

 spermatogonia the protoplasmic separation is not very complete. 

 The spermatides have a large granular nucleus and a narrow rim of 

 protoplasm, and sometimes exhibit slow amoeboid movements. From 

 the protoplasm a primary sperm filament or tail grows out as 

 a process. The granular substance of the nucleus retii'es to the 

 periphery and becomes crescentic, while in the protoplasm an 

 " accessory corpuscle " (" Nebenkern") is formed, whether from the 

 nucleus or not, Herr Platner was unable definitely to determine. In 

 Arion the accessory body has the appearance of a polyhedron formed 

 of 4-6 rods, in Helix it forms an irregular circular, subsequently 

 coiled figure. The nucleus of the spermatide forms itself anew, and 

 exhibits a peculiar invagination, becoming sack-like ; the uncoloured 

 internal portion of the sack forms the axial portion of the future head, 

 and is continued backwards into the above-mentioned extra-cellular 

 primary tail. The intra-cellular portion grows in length and becomes 

 bent, or sometimes even spirally twisted, the head also stretches 

 and pushes out of the cell, the protoplasm and the accessory body come 

 to lie ever further and further back along the primary tail, the final 

 result being that the accessory body degenerates and the protoplasmic 

 sheath acquires the definite structure of two (in Helix three) 

 threads coiled round the axial filament or primary tail. The 



E 2 



