ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 31 



Proneomenia sluiteri.* — Dr. A. A. W. Hubrecht gives a full 

 anatomical account of this interesting archaic Mollusc, the discovery 

 of which we have already noted, "j" There are no external appendages ; 

 the groove enclosing the foot is indicated by a dark longitudinal 

 line, the mouth and anus are at either extremity. The integument 

 is stiff owing to the presence of several layers of spicules of 

 carbonate of lime ; externally to the circular layer there is a cellular 

 one, which appears to be the matrix of the integument ; and 

 there is an interspicular substance which is homogeneous and 

 structureless, and appears to be of a chitinous nature. The youngest 

 spicules are found quite close to the deep cellular layer of the 

 matrix ; the older ones are in communication with this layer 

 by radiating cords of connective tissue, and the points of the inner- 

 most project towards the exterior. So far there are certain im- 

 portant differences between this form and Neomenia, and, in the 

 latter, blood-vessels find their way into the skin ; moreover, in 

 Proneomenia at the hinder end of the body there are two symmetri- 

 cally developed cteca connected with the anal cavity, and containing a 

 special secretion ; they are provided with a strong muscular invest- 

 ment, so that, whatever their homology or functions may be, there 

 can be no doubt that at times their contents may be forcibly 

 expelled. 



In his account of the muscular system the author states that 

 in Proneomenia, as in Neomenia, the stronger muscular fibres are 

 enclosed in a delicate sheath of connective tissue, which forms trans- 

 verse folds and so gives to the muscle the appearance of being 

 striated. The most anterior portion of the ventral groove leads 

 into a system of ciliated slits and cavities which ramify and com- 

 municate with one another ; the whole would seem to form a gland — 

 the " anterior foot-gland." The posterior foot-gland has no ciliated 

 cavities. 



The nervous system truly belongs to the type of the Amphineura; 

 the single cephalic ganglion is comparatively very small ; it gives off 

 three separate pairs of principal trunks, the innermost of which forms, 

 as in Chiton, a sublingual commissure ; the second pair surrounds the 

 pharynx and developes the anterior pedal ganglia; the third pair 

 gives rise to the longitudinal lateral nerves, and "a regular series 

 of commissures similar to those between the two pedal nerves, 

 connect the two lateral with the two pedal nerves." The study of 

 the details of the nervous system reminds Dr. Hubrecht that all late 

 investigations into the lower Invertebrates appear to point towards 

 an increased complication of the commissural connections, culminating 

 in the direct continuity of nervous tissue throughout more or less 

 extensive regions of the body. It is remarkable further, that " the 

 lower we descend m the Molluscan subdivision the more a system of 

 transverse commissures between the longitudinal connective stems 

 fixes our attention." Perhaps, indeed, the earlier Mollusca had their 

 nervous system plexiform in arrangement. Further, the fact is of 



* Niederl. Arch. f. Zool., Suppl. Band I., ii. (1881) 75 pp. (4 pis.), 

 t See this Journal, i. (1881) p. 28. 



