832 



SCIENCE. 



[Vol.. II., No. 47. 



<'ranules, and a large central mass to be regarded as 

 tlie nucleolus. One specimen was found with nuclei 

 in various stages of division. It appears that the 

 nucleolus separates into two parts, between which, 

 across the equator of the nucleus, appears a partition. 

 Similar processes were observed in another Amoeba 

 (sp.?). In these cases we have a form of nuclear di- 

 vision somewhat different from any hitherto observed ; 

 in that the nucleolus divides first, and the partition 

 between is formed without the participation of the 

 nuclear membrane. 



Biitschli has asserted that in Amoeba proteus (prin- 

 ceps B. ) the nuclei are either small and numerous, 

 or large and few. Gruber has found them always of 

 about the same size, and very variable in number 

 and relative proportion to the bulk of the individual. 

 — {Zeitschr. wiss. zooL, xxxviii. 372.) c. s. M. [570 



Coelenterates, 



The nervous system of the Siphonophores. — 



According to Korotneft, who has studied the minute 

 anatomy and histology of the Siphonophores, the Dl- 

 phyidae are the least modified, and present the most 

 primitive or ancestral structure. In them the ecto- 

 derm is a simple muscle-epithelium with well-devel- 

 oped muscle-fibrillae, which lie npon muscle-septa, 

 or outgrowths from the supporting layer. 



A more highly differentiated organization is found 

 in the Apolemiadae. The epithelial cells are uearly 

 separated from the muscle-fibrillae, towhich they are 

 united only by fine protoplasmic threads. Between 

 the muscle-septa the epithelial cells are folded over to 

 form an open furrow, which is floored with cells a 

 little larger than those over the general surface of the 

 body. 



In the Agalmidae the cells in this furrow are en- 

 tirely covered up by the ordinary surface-epithelium. 

 They are very large, are united by processes to the 

 muscles, and they constitute a true central nervous 

 system formed by involution of the ectoderm. The 

 muscle-fibres of the Agalmidae are entirely separated 

 from the epithelial cells, and the latter are flattened. 

 Korotneff has traced the origin of the nervous system 

 in the embryo. In a Forskalia larva there is no trace 

 of nerve-cells ; and the epithelio-muscular layer, the 

 muscle-septa, and the endoderm are like the corre- 

 sponding structures of Diphyes. 



As the animal grows, these ectoderm-cells, which lie 

 between the muscle-septa, grow larger, sink down, 

 and become covered up by the ordinary surface ecto- 

 derm-cells. They then throw off processes to the 

 muscle-fibres, and thus become converted into the 

 nervous system. The nerve-cells are therefore, so 

 far as their origin is concerned, epithelio-muscular 

 cells, and they so far lend support to Kleinenberg's 

 neuro-muscle theory. 



Korotneff describes sensory cells in the region of the 

 nervous system of the Agalmidae, and also in the air- 

 bladder. These sensory cells are muscle-cells which 

 still retain their primitive position on the surface; 

 and they are furnished with sensory hairs, and are 

 joined by processes to the muscle-fibrillae. 



In the Physophora the ectoderm has been special- 



ized in two ways. On the stem the cells have the 

 morphological characteristics of nerve-cells and the 

 position and arrangement which characterize muscle- 

 cells: they are neuro-epithelio-muscular cells. There 

 are also many sensory cells arranged in longitudinal 

 rows among the ordinary cells; but there is no in- 

 folded nervous system upon the stem, as there is in 

 the Agalmidae. This is to be found, however, upon 

 the air-bladder, which is thickly covered with nerve- 

 cells. On the upper surface of the bladder these are 

 directly united to the surfacecpitheliuui, while upon 

 the lower surface they are directly united to the 

 muscles. He says that there are physiological reasons 

 (which are not stated) for believing that the upper 

 nerve-cells are sensory, and those on the lower sur- 

 face motor. 



He speaks very briefly of the diffused nervous sys- 

 tem of Porpita; and his observations apparently 

 agree with those recently published more at length 

 (see Science, ii. 396) by Conn and Beyer. — {Zool. 

 anz., 148.) vv. k. b. [571 



Worms. 



Systematic papers on w^orms. — Dr. -K. v. 

 Drasche has taken advantage of the preservation of 

 all Diesing's and many of Molin's original specimens 

 of nematods in the Vienna museum to draw up fresh 

 and more accurate diagnoses of the species described 

 by these authors, and also to give a good many new 

 figures. This labor is calculated to avoid much con- 

 fusion which might otherwise arise from the very 

 imperfect character of the original descriptions. — 

 (Verh. zool-bot. r/es. Wien, xxxii. 117.) 



The same author also describes some new ascarids 

 collected in Brazil by Natterer, and adds some notes 

 on Ascaris ovis and A. rigida. — {Idem, 139.) 



G. M. R. Levinsen has published the first part of a 

 valuable revision of northern Annulata, Gephyrea, 

 Chaetognathi, and Balanoglossi. He attempts chiefly 

 to describe the species, elucidate their histoiy in sci- 

 entific writings, and their geographical distribution. 

 The essay contains full synoptic tables. The work 

 was undertaken at the request of Prof. Steensti-up 

 and Dr. Liitken. — ( Vidensk. meddel. nalurh. forcn. 

 Kjubenhavn, 1SS2, 160.) c. s. M. [572 



Pentastomum from an Alligator lucius. — J. 

 Chatin has found Pentastomum, probably P. oxy- 

 cephalum, in the liver of a caiman. This is a new 

 locality for the parasite. He gives an excessively 

 prolix general account of the anatomy of the animal, 

 but contributes little that is new. The booklets 

 around the mouth have a stalk, and three movable 

 claws thereon, — two at the sides near the end, the 

 third terminal. The author denies the cellular char- 

 acter of the epidermis: it is ' formed merely by a mass 

 of protoplasm in which are scattered numerous nuclei.' 

 (It can hardly be questioned that this is a mistake 

 due to superficial observation. The author gravely 

 adds his doubts as to the cellular constitution of the 

 epidermis in arthropods generally. In this he is singu- 

 larly unfortunate; as there is hardly any f.act in insect 

 histology more easily verified, even by inexperienced 

 students, than the existence of epidermal — so-called 

 hypodermal — cells. The error of describing an epi- 



