ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 8i5 



in their function, tlie former being the organ in whicli develop- 

 ment is accomplished, and commencing at that point on the generative 

 tract at which the characters of the contents change, where the 

 spermatozoa are accumulated in great numbers, and where the ova 

 undergo fertilization. In the epithelial layer there is a remarkable 

 development of papilliferous projections, with corresponding grooves ; 

 into the latter the spermatozoa seem to make their way, and so escape 

 from the current which would drive them outwards. The conjunctivo- 

 muscnlar layer of the duct has been only incompletely studied, but 

 van Beneden points out its great importance as being possibly the 

 representative of the splanchnic layer of Nematodes ; in other words, 

 the brothers Hertwig are perhaps right in regarding the Nematoda as 

 Enterocoelia. This consideration is the more valuable when we know 

 that, in the adult, there is no trace of any fibrous intestinal layer in 

 the walls of the digestive tube. " If the splanchnic origin of the 

 conjunctivo-muscular tunic of the sexual apparatus is demonstrated, 

 it is probable that the secondary disappearance of the coelomic ej)ithe- 

 lium from the outer side of the intestine, will be established at the 

 same time. 



New Worm with Remarkable Nervous System.* — The ' Willem 

 Barents ' on her third voyage captured a worm, which A. A. W. 

 Hubrecht describes under the name of Pseudonematon nervosum. He 

 gives a general account of its structure, and promises a fuller mono- 

 graph. The animal is about 65 mm. long. If mm. thick, tapering 

 behind. The digestive tract runs straight through from end to end. 

 On the ventral side, about 45 mm. from the head, is a disk, probably 

 a sucker. No traces of sexual, excretory, or sensory organs were 

 found. The epidermis is thin. The muscles form three layers, a 

 thick external longitudinal, a middle transverse or circular, and an 

 internal longitudinal layer, variously developed in different parts of 

 the body. The nervous system is very remarkable ; it forms a con- 

 tinuous layer completely around the body, and lies immediately inside 

 the layer of cii'cular muscular fibres. It consists (1) of a fine 

 network of delicate filaments, appearing as if felted, barely tinged 

 by the staining reagents, and (2) of scattered nuclei belonging 

 partly to connective tissue, partly to ganglion-cells. The layer 

 forms a continuous tube from the head, where there is no ganglionic 

 enlargement, back through the body to the caudal region, where the 

 layer is present dorsally only. 



Hubrecht further discusses the phylogeny of the nervous system 

 in continuation of his previous paper.f He points out, that (1) in 

 its lowest forms (Medusse), the nervous system is difluse, and there 

 are no nerve-fibres properly so-called ; (2) in a little more advanced 

 stage it tends to form a layer spread out under and parallel with the 

 ectoderm ; the general histological character is the same as under (1) 

 — a felted network of fine fibrillse, which spring from the ganglion- 

 cells {Adinioe, Pseudonematon) ; (3) tlie diffuse layer is still present, 

 but certain tracts are more developed, making the pirimitive nerve- 



* Verb. Akad. Wetensch. Amst., xxii. (1883) Art. 3. 

 t Quart. Journ. Micr. Sci., xx. (1880) p. 43l'. 



