ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. • 591 



the head-zone, in which four trunk-segments are formed anew behind 

 the head, the mesoderm arises in all probability in the same way as in 

 the trunk-zone. The mesoderm forms the longitudinal, pharyngeal, and 

 setal musculature, the peritoneum, and the nephridia. 



The ectoderm forms the circular musculature and the nervous 

 system. At the posterior end the primordium of the nervous system 

 coalesces with the ectoderm ; the same is seen in the trunk-zone, where 

 a new foundation for the nervous system is formed, uniting anteriorly 

 with the old ventral nerve-cord ; in the head -zone there is an elongation 

 of the ventral cord, and the oesophageal commissure and brain arise by 

 paired ectodermic proliferations on the lateral lines and on the ventral 

 setal follicles. 



The pharynx is a product of the endoderm. The new mouth 

 rises by invagination of the ectoderm to meet the gut, and the new 

 proctodamrn is a simple coalescence of gut and epidermis. 



Nematohelminth.es. 



Structure of Nematodes.* — Max Rauther has investigated the 

 structure of the oesophagus in numerous free-living Nematodes, and 

 has also studied the localisation of the excretorv function. The indiero- 

 carmin absorbed by the skin or taken with the food is not collected for 

 elimination in any glands, but between the radial fibres of the oesophageal 

 musculature and in the most anterior and most posterior region of the 

 mid-gut. The excretion is thus indirect ; the function of the oesophagus 

 may be compared to that of a Mammalian glomerulus, and that of the 

 mid-gut to that of the absorbing renal canaliculus. The author con- 

 trasts the excretion of free-living Nematodes with that of parasitic 

 forms. 



Development of Nematodes.! — E. Martini has studied Pseudalius 

 minor, Cucullanus elegans, Nematoxys ornatus, and Rhabdonema nigro- 

 venosum. Organ-forming areas or cells can be recognised very early 

 in development, even at the 8-cell stage. Segmentation results in 

 450-500 elements. A primordium of the gut appears during or imme- 

 diately after segmentation, and is separated from the outermost cell- 

 layer by a groove open dorsally. The definitive epithelium of the 

 surface of the body is produced by six longitudinal rows of cells in 

 the middle and posterior part of the dorsum. The bodies and nuclei 

 of these cells pass into the longitudinal lines, especially in the lateral 

 areas. From the two lateral portions of the groove the four muscle- 

 bands are differentiated. 



ChaBtosomatidse.j — A. Schepotieff discusses these peculiar Nematode- 

 like marine worms, and defines five species of ( 'hcetosoma. Among the 

 peculiarities may be noted : the distinct head-region, the ventral rows 

 of bristles, and the division of the body into an anterior narrower and a 

 posterior broader region. The composite mobile seta) resemble those of 

 Desmoscolecidse, but the genus Rhabdogaster which Schepotieff has 



* Zool. Jahrb., xxiii. (1907) pp. 703-40 (1 pi. and 7 figs.). 



*■ Zeitschr. wiss. Zool., lxxxvi. (1907) pp. 1-54 (3 pis. and 2 figs.). 



j Zool. Jahrb., xxvi. (1908) pp. 401-14 (2 pis.). 



