ZOOLOGY AND BOTANY, MIOROSOOPY, ETC. 755 



With regard to the resemblances between vertebrate and invertebrate 

 nervous systems, we must for the present be content with general points of 

 coincidence, and must rigorously refrain from detailed comparisons. If we 

 take the Nemertean arrangement as our starting-point, it is easy to under- 

 stand the polymerous root of the vertebrate vagus and its mixed physio- 

 logical duty. The author enters at some length into a comparison of the 

 Chordate and Nemertean nervous systems. The origin of metamerism is 

 looked for in the dangers to the rupture of individuals and their counter- 

 action by regenerative processes. 



Spermatogenesis in Nemerteans.* — Mr. A. Bolles Lee communicates 

 an account of the spermatogenesis of nemerteans, especially of Tetrastemma 

 melanocephalum. His research has special reference to Sabatier's theory 

 of spermatogenesis. According to Sabatier the primitive " male ovule " 

 developes on its surface a number of " protospermoblasts " round a degene- 

 rating (female) core, the " protoblastophore," and in each of the proto- 

 spermoblasts the same process is repeated in the development of a second 

 generation of centrifugal elements — the " deutospermoblasts " which are 

 disposed around the central core or " deutoblastophore." This account the 

 author was entirely unable to verify. 



He is inclined to believe that the male elements have their primary 

 origins from mesodermic tissue, and not, as Hubrecht maintains, from the 

 ectoderm. (1) What Sabatier has described as a mass of non-nucleated 

 protoplasm, was the first certain trace of the male elements recognized by 

 Bolles Lee. But when this apparently homogeneous content of a sperm- 

 sac was fixed, stained, and sectioned, it was found to consist of a mass of 

 distinctly nucleated cells. (2) At a later state a median section of one of 

 the lobes of a sperm-sac exhibited from the periphery centralwards, the 

 following series of cell groups : — (a) One or two layers of large pale cells, 

 distinctly separate, with pale nuclei ; (b) a much larger region with 

 smaller, more crowded cells, with more distinctly chromatic nuclei, and 

 more or less regularly linked together by strands ; (c) within this sperma- 

 tozoids, more or less adherent, with their heads towards the periphery and 

 their tails in the lumen. This appearance is interpreted as a succession of 

 spermatogonia (S^), spermatocytes (S^), spermatides, and spermatozoa from 

 the periphery inwards. 



(3) The author next discusses the minute characters of these different 

 stages which were studied in preparations fixed with osmic acid vapour. 

 The elements S^ are typical cells ; no trace of karyokinesis was seen ; but 

 traces of binary division and certain indications of endogenous multiplica- 

 tion were observed. The elements S^ are much smaller, but distinctly 

 cellular, with very thick nuclear ribbon, either uniform or necklace-like. 

 Some of the dispositions suggested very simple karyokinetic division. 

 They also multiply by endogenous division. The spermatides are at first 

 very small, but seem to increase notably in size before becoming spermatozoa. 

 They have a cellular membrane, but only a minimum of protoplasm. 

 Neither here nor in S^ was a nuclear membrane demonstrable. The 

 changes of the nucleus, the appearance of the accessory body or " Neben- 

 kern," the formation of the tail and other modifications in the ontogeny of 

 the spermatozoid are then discussed. Young sperms were seen swimming 

 about with a suspended vesicle, the remnant of the cell-membrane con- 

 taining a homogeneous substance, and sometimes the " Nebenkern " intact 

 or in process of dissolution. The author believes that the membrane is not 



* Kec. Zool. Suisse, iv. (1887) pp. 409-30 (1 pi.). 



