ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 327 



cast. The preparations thus made corresponded so exactly in every 

 detail with the problematical bodies from the Cambrian, that no doubt 

 could exist as to their identity. The stars and pyramids are casts of 

 the gastrovascular systems of the Medusae, the rays of the stars and 

 the angles of the pyramids correspond with the arms, and the 

 crescent-shaped projections occasionally occurring between the angles 

 are casts of the genital cavities. The impressions on the slabs of rock 

 are produced by Medusas thrown on the shore, and which, sinking 

 more or less into the soft ground by their own weight, make a more 

 or less complete impression of the body-cavity. The bodies lying 

 free in the clay were probably produced by Medusee which lay on 

 their backs, their gastrovascular system becoming filled up with sand 

 or mud. There are some Medusas which do not swim, but sink into 

 the mud on their backs, and lie still watching for their prey. 



The fact that the number of rays in these fossils varies from 4 

 to 5 is not an objection to their medusoid nature because in the 

 present day individuals are found with 5, 6 or 9 rays. Certainly 

 this deviation from the normal number appears more frequently in 

 the Cambrian Medusae than in the existing sjpecies. 



The impression of the disk and traces of the tentacles are still 

 distinctly seen round a four-rayed star on a rock from Lugnas. 

 Many slabs are covered with thick, spiral, vermicular bodies, which 

 Nathorst considers to be arms torn from Medusae. Certain thread- 

 like marks on sandstone were supposed by him to be made by 

 swimming Meduste that grazed the ground with their tentacles. He 

 was also of opinion that the so-called Eophytes, which occur in 

 great quantities in the same strata as the Medusae fossils, were 

 without doubt produced by creeping Medusee. 



The following species of Medusae from Lugnas have been dis- 

 tinguished by him : (1') Medusites radiatus Jjinnars. sip. ; (2) Medusites 

 favosus n. sp. ; (3) Medusites Lindstr'dmi Linnars. sp. 



Hitherto Medusae were only recognized with certainty in the 

 Solenhofen slate, and the discovery of Nathorst is therefore of 

 great interest. It is especially interesting also because these 

 Medusae occur in the deepest strata that have ever produced fossils, 

 so that they must be reckoned as amongst the oldest animals whose 

 tracks are known to us." 



Lymph of Invertebrates.* — C. ¥. W. Krukenberg obtained 12-14 

 drops of pure lymph from a medium-sized Hydrophilus piceus; he 

 fi.nds that the lymph varies remarkably in different individuals, the 

 colour being different even when the specimens have lived under the 

 same conditions. The coagulation which is spontaneously formed in 

 it is, compared with that of the htemolymph of MoUusca and Crustacea, 

 of a more membranous nature, and not gelatinous ; the lymph under- 

 goes coagulation at a comparatively low temperature. The melanotic 

 change of colour presents remarkable individual variations, which lead 

 to the belief that the body which blackens immediately on exposure to 

 the air is in certain cases preformed in the circulating lymph. The 



* Verb. Nat. Med. Ver. Heidelberg, iii. (1881). 



