ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
313 
thing, the position of the united nuclei defines the position of the large 
animal cell. The amoeboid movements of the ovum cease with the 
formation of the nuclear spindle. This spindle always lies in the longi- 
tudinal plane of the ovum ; the particular rotation or taxis by which it 
takes up this position is discussed at length. An interesting periodicity 
in the cleavages is demonstrated, and their history is followed on the 
128-cell stage. 
Parasitic Nematodes.* — Dr. A. Railliet describes the structure and 
life-history of 140 species of Nematodes, chiefly those which are parasites 
in man and domestic animals. 
Platyhelminthes. 
Monograph of Nemertines. t — Dr. 0. Burger has added to the Naples 
series a massive monograph on Nemertines. He begins with the usual 
historical survey, in which the names of McIntosh, Hubrecht, and J oubin 
figure prominently, and he gives an index to all genera and species, and 
their synonyms. 
The first division of the anatomical portion deals with the general 
structure of Nemertines, working from the morphologically simple types, 
e. g. Carinina, to the more complex forms. The second division is 
devoted to histological details. We follow the author’s own summary. 
The skin is represented by an epithelium with a gelatinous basal 
layer, or, instead of the latter, a glandular cutis, often with musqle-fibres. 
The epithelium consists of ciliated and glandular cells, and is often 
wholly glandular, e. g. in Carinella, near the genital pores at the period 
of sexual maturity. It contains hook-like bodies in Eunemertes echino - 
derma, crystals or calcareous corpuscles in Geonemertes , and muscle- 
fibres in Carinoma. 
The cutis is often divided into an outer glandular and an inner 
connective layer, the latter represented by gelatinous tissue in the 
transparent forms, both often including longitudinal muscle-fibres. 
In Proto-, Meso-, and Metanemertini, the muscular sheath consists of 
a circular and a longitudinal layer, often with diagonal fibres between 
them. In Heteronemertini there is also an external longitudinal layer, 
and then the diagonal fibres, if present, lie between this and the circular 
layer. Each fibre is a nucleated cell ; the striping, often visible in the 
muscular layers, depends on ampullations of the fibres. 
There is no body-cavity. A parenchyma of gelatinous appearance 
surrounds the organs ; it exhibits nuclei, and sometimes (e. g. around 
the rhyncho-coelom and blood-vessels) distinct cells, and is traversed by 
dorso-ventral muscle-strands or plates. 
Except in Malacobdella the gut is straight. The mouth may be 
either behind or in front of the brain. In the latter case it usually opens 
into the rhynchodaeum. The anus is frequently at some distance from 
the posterior end on the dorsal surface ; the fore-gut is very rich in 
glandular cells, which are absent elsewhere ; the mid-gut of the higher 
forms has lateral pockets, alternating with the genital sacs ; the hind-gut 
* ‘ Traite de Zool. Medicale et Agricole, ’ 2nd ed., Paris, 1895, pp. 388-562, 
figs. 255-385. Review in Zool. Centralbl., iii. (1898) p. 207. 
f * Die Nemertinen des Golfes von Neapel und der angrenzenden Meeres- 
Abscknitte,’ in ‘ Fauna und Flora des Golfes von Neapel,’ Monograpliie xxii. 
Berlin, 1895, 4to, 743 pp. and 31 pis. 
