ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 27 



auditory); (3) the cerebral; (4) the posterior (branchial) ; (5) the 

 visceral ; and (6) the caudal. The brain of the adult Tunicate arises 

 from the union of the first ganglia. As to the segmentation of the 

 nervous system in Tunicates, it is a matter of appreciation. 



/3. Polyzoa. 



Spermatogenesis.* — M. A. de Korotneff finds in Alcyonella fongosa 

 a very fit object in which to study the process of spermatogenesis. The 

 succession may be summed up in La Valette St. George's familiar 

 formula, spermatogonia give rise to spermatocytes, these become 

 spermatides and mature into spermatozoa. 



The young endodermic cells of the funiculus of a bud have spherical 

 transparent nuclei. These contain nucleoli and these alveoli. The 

 nuclei of these spermatogonia multiply without trace of karyokinesis. 

 Multinuclear cells result, the nuclei being situated just below the 

 'cellular membrane. The individual spermatocytes bud off spermatides, 

 and the whole mass comes to have the appearance of a transparent 

 vesicle covered superficially by a thick layer of maturing sperms. 



The external surface of the peripheral (outer) end of each nucleus is 

 surrounded by a homogeneous sheath, which gives off a process forming 

 the central filament of the tail. The internal surface of the nucleus has 

 a gradually thickening cap of protoplasm. The first-mentioned sheath 

 acquires a swollen vase-like form, and after certain modifications becomes 

 the neck of the spermatozoon. The internal cap separates from the 

 nucleus, and becomes gradually conical. The nucleolus, a small well- 

 defined spherule, becomes finally lodged in this cap, where it is pro- 

 tected, and forms the essential part of the head. The details are 

 minutely described. 



M. Korotneff suggests, in regard to the peculiar sperm of Ascaris 

 megalocephala, that the caudal portion is the head-cap, and its nucleus 

 really the nucleolus. The other portion contains a number of filaments 

 plunged in a protoplasmic mass ; these structures may be identified with 

 the tails of other spermatozoa, and compared, for instance, with the 

 processes seen in the crayfish sperm. 



Fresh-water Bryozoa.j — Herr M. Verworn has investigated the 

 structure and development of Cristatella. He finds that the chief 

 anatomical peculiarities are the presence of a movable pedal disc on 

 which the individuals are arranged in parallel rows, the complete 

 absence of an ectocyst and of a fold of the endocyst ; as a consequence 

 the anterior and posterior parieto-vaginal muscles have disappeared ; 

 there are a comparatively large number of tentacles. 



The author adopts provisionally the view of Krapelin that the 

 whole outer cell-layer of the integument is formed by ectoderm, the 

 inner lining of the body-cavities by mesoderm, and the inner epithelium 

 of the enteric tract by endoderm ; embryological investigations are, how- 

 ever, needed on these points. The pedal disc consists of an outer ecto- 

 dermal layer, a median muscular layer, and a mesodermal pavement 

 epithelium. The first of these has, in addition to large vesicular cells 

 and others containing a clear slimy mass, long cylindrical glandular 

 cells with a broad base on the lower surface and at the sides ; between 



* Comptes Remlus, cv. (1887) pp. 953-5. 



t Zeitschr. f. Wiss. Zool., xlvi. (18S7) pp. 99-130 (2 pis.). 



