INVERTEBKATA, CRYPIOGAMIA, MICROSCOPY, ETC. 727 



side of the interior of tliis cavity, and parallel to the long axis of the 

 cell, are a number of distinct transparent homogeneous filaments inserted 

 above and below into the ordinary granular protoplasm which consti- 

 tutes the remainder of the cell. In a teased preparation some of these 

 cells are easily found in a state of rapid rhythmical contraction, 

 giving as many as 100 to 180 energetic beats per minute. Tlie form 

 of the cell alters with every pulsation, shortening and broadening like 

 a contracting muscle. This change of form is simply imi)ressed upon 

 the cell-body by the contraction of the internal fibres, and does not 

 therefore truly correspond to that observed in a muscle. Some cells 

 also of extreme curvature (for hardly any two are quite alike) bend 

 sharply and return with a spring. The movements soon become slow 

 and incoordinate, and waves can be seen passing along the separate 

 fibres independently of each other. The movement stops altogether, 

 and the cell bursts, but the fibres resist for some time longer the 

 destructive action of the water. 



Mr. Geddes was never able to observe any rhythmical contraction, 

 but at most a feeble quivering within the cell while in the body of the 

 animal, nor to make out any trace of definite arrangement. Max 

 Schultze has described how the alimentary canal of the higher Plana- 

 rians swarms with OpalincB, and it is possible that these so singular 

 structures may be excessively modified parasitic Infusoria. In any 

 case, the main histological interest lies in the fact that these pulsatile 

 cells cannot be classified either with ciliary or amoeboid, with plain or 

 striated muscular cells, but present a distinct type of contractile 

 structure. 



Planaria Limuli.* — Dr. Graff points out that the Planarian para- 

 sitic on Limulus (the American king-crab), and so well entertained as 

 to be present in large numbers (" more than one hundi-ed ") on it, is 

 not the same as Planaria angulata. Somewhat similar in appearance 

 to P. lactcea, it differs from it by its pointed anterior end, and by the 

 possession of a large posterior sucker. The bilobed cerebral mass 

 has an eye, on either side, suj)ported by a pyriform swelling ; the eye 

 is covered by black pigment, and the lens is expressly stated (in 

 ojiposition to Minot) to be made up of a number of cells, as it is in 

 all fresh-water Planariaus and in all Khabdocoela which Dr. Graff has 

 examined. The longitudinal nerve-trunks are well develoi^ed in this 

 new species, and are united at the posterior end, above the sucker, 

 without any diminution in size ; from their point of union delicate 

 nerve-branches are given off to the sucker ; the longitudinal trunks 

 give off lateral branches at regular intervals, and, corresponding to 

 these, there are transverse anastomoses, so that a complicated mesh- 

 work of nerves is to be observed in these creatures. Development is 

 effected without any metamorphosis, and within the cocoon ; in em- 

 bryos i mm. long the enteric tract is not differentiated, and the 

 cerebrum has the form of two transversely-set, oval masses of cells. 

 The eyes first ajjpear when the embryo is 1 mm. long. Each cocoon 

 contains from two to nine embryos, and forms a yellowish-brown 

 oval capsule, about 3 mm. long and 1^ mm. broad, while it has a 

 * ' ZopI. Anzeiger,' 11. (1879) p. 202. 



