212 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Structure and Development of the Visual Area in the Trilobites.* 

 — Mr. J. M. Clarke has made an interesting addition to our knowledge 

 of the eyes of Arthropoda by an account of those of the common fossil 

 JPTiacops rana. In many cases both cornea and seleron are normally pre- 

 served ; in others one alone is retained ; in others both may be removed, 

 leaving pillars of the matrix with cup-shaped surfaces, each bearing a 

 little ball at the centre ; an external film may be removed from the 

 entire visual area, destroying the cornea, or, lastly, silica may be 

 deposited as a thin film upon or replace a thin film of the external 

 and internal surfaces of the test, and all the rest of the substance of the 

 test and matrix may be removed. 



Mr. Clarke thinks that the schizochroal eyes of the Trilobites are 

 aggregated, and not properly compound eyes. The visual organs of 

 Harpes may prove to be of similar character. The scleral portion of 

 the visual surface is of the same structure as the test, and is a direct 

 continuation of it. There is no evidence of any continuous corneal layer 

 covering the entire surface. The corneal lenses are wholly discrete 

 from the epidermis, but are of epidermal origin. In the addition of new 

 lenses to the visual surface, they appear to arise from a thinning of both 

 surfaces of the integument. The corneal lenses were hollow or were 

 filled with some matter not homogeneous with the cornea itself. The 

 corneal lenses, and, therefore, the ommatidia were added to the visual 

 surface with advancing age until the mature growth of the individual 

 was attained; thereafter they diminished in number with increasing 

 senility. The addition of corneal lenses occurred regularly at the 

 extremities of the diagonal rows. No evidence is preserved of crystalline 

 cones in the ommatidial cavities, but they may have been removed in 

 the decomposition of the soft parts of the ej'e. 



With regard to the suggestion of Dr. J. S. Kingsley, in his paper on 

 the eye of Crangon, that the mere fact of invagination indicates an 

 ancestral condition, Mr. Clarke states that in Mesothyra oceani, one of 

 the largest known representatives of the Phyllocarida, the eye consists of 

 a simple deep pit at the summit of the optic node. There is no evidence 

 that this pit contained a series of lenses, but it may serve as the ancestral 

 condition of the Decapod eye. 



Migrations of Pentastomum denticulatum in Cattle-t — Dr. V. 

 Babes had in the summer of 1888 the opportunity of examining some 

 thirty-five cattle which had died of epidemic hsemoglobinuria. In all 

 but one instance he was able to verify the existence of the Pentastomum 

 denticulatum. He found numerous specimens of the parasite in the 

 mesenteric glands and between the two peritoneal layers of the me- 

 sentery; while in the convexity of the intestinal coils he met with 

 roundish nodules about 5 mm. broad, and often arranged at regular 

 distances. These nodules contained a living Pentastomum larva. As 

 the parasite advances in development, so it proceeds towards the lumen 

 of the intestine, the perforation of the mucosa being accompanied by 

 haemorrhage. In one case hundreds of parasites were found free in the 

 intestinal canal. 



It sometimes happened that living examples were not discovered 

 either in the glands or in the intestinal walls, but the glands were found 



* Journal of Morphology, ii. (1888) pp. 253-70 (1 pi.). 

 + Centralbl. f. Bakteriol. u. Parasitenk., v. (1889) pp. 1-5. 



