ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 725 



back shifted blastomeres to the normal position, or at any rate to such a 

 position that they are able subsequently to produce a larva deviating 

 only slightly from- the normal. The elucidation of this factor must be 

 the object of further experiment. 



Structure of Cephalothrix.* — G. Wijnhoff publishes the first of a 

 series of papers on the genus Cephalothrix, and its significance for the 

 classification of Nemerteans. The present paper deals with the anatomy 

 of the genus. The general results are as follows. The single-layered 

 skin-epithelium exhibits unicellular (hasmatoxylin) glands in the region 

 of the foregut, but these show no tendency to form packets. The inner 

 circular muscular layer of G.filiformis has preserved all the characters 

 of an integumentary muscular sheath, for it surrounds all the organs, 

 even the gonads. All the species investigated have a longitudinal 

 muscular plate. Connective-tissue is only developed in the region be- 

 tween the brain and the mouth. In the nerve-tissue of the head there 

 is a head-gland which suggests the glandular layer of Gallinera. There is 

 no difference between a head-gland and " submuscular glands." The 

 proboscis has differentiated in the same way as that of Gallinera, and 

 indicates a remote relationship also with Carinomella, and possibly with 

 some primitive Heteronemerteans. 



In G.filiformis there is a circular musculature peculiar to the foregut. 

 A true hind-gut is lacking in all Nemerteans. No true intestinal pouches 

 are present. The two blood vessels anastomose only dorsally in the 

 anterior portion of the head, and beneath the anus. The nephridia are 

 not connected by a longitudinal canal, but each terminal bulb opens 

 through an excretory duct to the exterior. The dorsal brain ganglia are 

 very strongly developed ; their fibre-nuclei are connected by lateral com- 

 missures with the ventral ganglia, but these are very slightly displaced 

 towards the ventral commissure. The dorsal brain commissure lies in 

 front of the ventral. The dorsal fibre-nuclei in species of Cephalothrix 

 show no tendency to bifurcation. There is a, subepithelial nerve-plexus 

 in the foregut, and in this two nerves have been developed beside the 

 oesophageal nerves. The anal commissure is ventral. The head -nerves 

 are homologous with the nerve-layer in Gallinera and Garinesta. Sharply 

 defined sense-organs do not occur in the genus Cephalothrix in the strict 

 sense. 



Hermaphroditism of Prosorochmus claparedi.f — G. Du Plessis 

 has proved that Prosorochmus claparedi Keferstein ( = Monopora 

 rivipara Salensky), is hermaphrodite. It is in many ways an interesting 

 Nemertean, 50-60 mm. in length, brightly coloured, and viviparous, 

 with the eggs hatching even in the interior of the ovaries. Small 

 and well-hidden testes occur irregularly between the intestinal sacs, in 

 animals which also show well-developed ovaries. There are two other 

 hermaphrodite species in the Mediterranean, viz. Tetrastemma marioni 

 and T. kefersteini, and the author suggests that Prosorochmus might 

 well be included along with Tetrastemma. In the fresh-water Stichostemma 

 eilhardi (Mont.), a small island of spermatozoa develops beside the large 

 ovum within the ovary. In all the Geonemertea there is hermaphroditism. 



* Zool. Jahrb., xxx. (1910) pp. 427-534 (4 pis.), 

 t Rev. Suisse Zool., xviii. (1910) pp. 491-5. 



