692 



SCIENCE. 



[Vol. II., No. 42. 



tainly five inches and three-quarters long. . It should 

 be stated that all of our American columbines that 

 have been studied, whether fertilized by bees, moths, 

 or birds, are strongly protandrous, like the European 

 species. — w. T. [394 



Symbiosis. — Dr. Sedgwick gives a -roell- written ^ 

 synopsis of the results of the more important recent 

 studies concerning the occurrence of chlorophyll in 

 animals, and its significance. These seem to show 

 that the so-called ' animal chlorophyll ' has uo actual 

 existence, being in every case (possibly excepting 

 Hydra and Spongilla) connected with a vegetable 

 structure living in the tissues of the animal. This 

 association of plant and animal, in the mutual bene- 

 fits derived, is held to be somewhat different from 

 the so-called parasitism known in lichens ; but it is 

 hard to see in what important respect the two cases 

 differ. — (Pop. sc. monthly, Oct.) W. t. [395 



ZOOLOGY. 



Coelenterates. 

 The anatomy and histology of Porpita. — A 



diffused nervous system, made up of a plexus of 

 scattered ganglion-cells connected with eacli other 

 by nerve-fibres, and similar to that described in the 

 Medusae and Actiniae by the Hertwigs, and in the 

 Hydn)ids by Jickeli, Lendenfeld, and others, has 

 been described by Chun in Velella. Conn and Beyer 

 have independently discovered the same structures in 

 Porpita ; although they express some doubt whether 

 they are really nerve-cells, rather than some form of 

 connective-tissue corpuscle without any nervous func- 

 tion. They incline, however, to the belief that the 

 close resemblance which they bear to cells which have 

 been found in the Medusae and Actiniae justifies 

 us in regarding them as a very primitive nervous 

 system. 



The cells in question are, in Porpita, ectoder- 

 mal; and sections show that they lie actually in the 

 ectoderm-cells, outside the supporting layer and the 

 layer of muscles. They are always found in connec- 

 tion with the muscles, and they are most abundant 

 where the muscular system is most developed. They 

 are bipolar, tripolar, or multipolar; and their pro- 

 cesses could be traced to a considerable distance. 

 Their distribution is as follows: they lie wholly in 

 the ectoderm; and their fibres, after running for a 

 considerable distance beneath the outer ectoderm- 

 cells and immediately upon the muscle-layer, finally 

 penetrate this layer, and are lost. The whole of the 

 upper surface of the animal is s\ipplied with them, 

 somewhat sparsely toward the centre, but much 

 more abundantly towards the edge, and especially in 

 the velum. The under surface of the velum has also 

 a rich supply, and the tentacles also contain great 

 numbers ; but towards the centre of the lower surface 

 of the disk they gradually disappear, and none could 

 he found upon the nutritive zooids. They are every- 

 where few in number, as compared with the ecto- 

 derm-cells, and they are very irregularly distributed. 

 There is nothing lilce a central nervous system, and 

 no union of the cells into a nerve-ring could be made 

 out. Conn and Beyer also describe a number of so- 



called 'sensory organs,' which are placed in pockets, 

 or pouches, around the edge of the velum. Each of 

 these is filled with large and highly modified ecto- 

 derm-cells, which the authors regard as sense-cells. 

 They have no connection with the ganglion-cells. — 

 (Stu.d. biol. lab. Johns Hopk. univ., ii. 433.) w. k. b. 



[396 



Visual organs of Solen. — Dr. Benjamin Sharp- 

 had been led to believe that Solen ensis and S. vagina, 

 the common razor-shells, are possessed of visual or- 

 gans, by observing that a number of these animals 

 which were exposed in a large basin for sale in Naples 

 retracted their siphons when his hand cast a shadow 

 over them. Eepealing the experiment at the zoologi- 

 cal station, he became convinced that the retraction 

 was due to the shadow, and not to a slight jar which 

 might have been the cause. Upon examining the 

 siphon, he found as many as fifty fine blackish-brown 

 lines or grooves between and at the base of the short 

 tentacular processes of the external edge. When a. 

 vertical section of these pigmented grooves is made, 

 the cells of which they are composed are fomid to be 

 very different from the ordinary epithelial cells of the 

 surrounding tissue. The pigment-cells are from one- 

 third to one-half longer than the latter, and consist 

 of three distinct parts. The upper ninth or tenth 

 part of each cell is jDerfectly transj^arent, and is not 

 at all affected by the coloring-matter used in making 

 the preparation ; the second part is deeply pigmented 

 and opaque, and forms about one-half the cell ; while 

 the remainder consists of a clear mass, which takes 

 a slight tinge when colored. This portion contains a^ 

 well-defined nucleus filled with granular matter, and 

 is probably the most active j^art of the cell. These- 

 retinal cells, if so they may be called, resemble thos& 

 of the very primitive eye of Patella. The value 

 to the Solen of an organ which would enable it to 

 detect the shadow of approaching objects as it lies 

 embedded in the sand, with the end of the siphon 

 protruding, must be evident; and the structure of the 

 cells described bear suflicient relation to those of the 

 eyes in Patella, Fissurella, and Haliotis, to make it 

 highly probable that they constitute true primitive- 

 visual organs. — (Acad. nat. sc. Philad. ; meeting 

 Nov. 6.) [397 



Organization of chitons. — A second part of Dr. 

 Bdla Haller's valuable investigations of the chitons 

 of the Adriatic has appeared. It is illustrated with 

 three double plates; and the species which have- 

 served his purposes are Chiton siculus and C. laevis. 

 This part is devoted especially to the finer structure- 

 of the buccal muscles, of the parts surrounding the 

 mouth and below the radula, and the minute struc- 

 ture of the branchia. He confirms the conclusion of 

 Dall in 1879, — that the separate branchial tufts cor- 

 respond each to a distinct branchia, instead of to the 

 old cyclobranchiate theory, — and adds very materi- 

 ally to our knowledge in each of the above-mentioned 

 directions. The author wisely refrains from much 

 theorizing, as no group of equal rank exhibits more 

 polymorphism than this, and no general rules can be 



