BY W. A. HAS WELL. 335 



As app«ai-s to be very generally the ease in the Aearida (Michael, 1895, 1894- 

 97; Thor, 1904), as well as in some other Arachnids (Bernard, 1894), the cells 

 or portions of. them, often become free in the lumen. As the contained blood 

 remains uncoagulated they are able to float freely, but in a few of my series, the 

 blood has for some reason undergone coagulation while the animal was still alive, 

 and in these cases the passage of the wandering cells from one side to the other 

 is plainly indicated by clean-cut cylindrical burrows through the coagulum (PI. 

 xssvii., fig. 14). The definitiveness of these and their straight, or nearly straight, 

 course, seem to indicate a distinct attraction or repulsion — ^not due to gravity, 

 since the direction of the canals is not the same on opposite sides. In a specimen 

 crushed while alive, moving enteric cells can sometimes be distinguished. These 

 assume the elongated narrow shape which they most habitually adopt in traversing 

 the enteric lumen. 



'I'he crayfish blood-corpuscles are ingested by the cells of the enteric epithe- 

 lium. This is quite clear in only one of my series of sections — one in which the 

 corpuscles are very strongly stained and the blood plasma and endoderm cells 

 not too strongly. It is certain of the latter projecting far into the lumen or 

 altogether detached that mainly discharge this function. In successive sections of 

 one of these cells I have counted as many as fifty of the corpuscles, some adlier- 

 ing to the surface, others half embedded, others more or less deeply sunk in the 

 cell-protoplasm. 



There are no intrinsic muscles in the wall either of the mesenteron or of the 

 excretory organ, and yet in the living animal, contractions occur in waves at 

 irregular intervals in the walls of both mesenteron and excretory organ. These 

 contractions must be due to a pair of strong muscular bands which extend 

 obliquely throughout the length of the body from the dorsal body-wall above the 

 anterior extremity of the excretory organ backwards and downwards, one on 

 either side of the excretory organ, between it and the corresponding mesenteric 

 caecum, to the neighbourhood of the excretory aperture. 



7. Salivary and cmti-comgulin Glands. 



There are in Astaeocroton three pairs of glands representing the "salivary" 

 series. If we adopt Thor's (1904, p. 105) nomenclature, these would correspond 

 to his tubular, reniform and dorsal — the last being perhaps the equivalents of both 

 anterior and posterior dorsal pairs, or perhaps of only one of them. The an- 

 terior and posterior oesophageal pairs and the unpaired tracheal are not re- 

 presented. 



By far the largest of these are the last — the dorsal. 'I'hese are about .3 mm. 

 in diameter, situated dorsally at the extreme anterior end of the body, just be- 

 hind the bases of the chelicerae, dorsal to the oesophagus and nerve-centre, fitting 

 close down over these structures and in close contact with one another in the 

 middle line. Each consists (PL xxxvii., fig. 13) of a group of large cells, about 

 .2 mm. in length, of approximately pyramidal shape, arranged around a central 

 cavity of variable extent — the beginning of the duct (d) — which is bounded by 

 their apices and is lined by a thin cuticle. Towards the broader end each cell is 

 composed of an almost homogeneous substance which is not very strongly affected 

 by staining agents; but, invading this near the apex, and sometimes spreading 

 throughout the greater part of the cell, is the accumulating secretion, which in 

 lightly stained sections appeai-s clear and yellowish, but in such as have been 

 strongly eosinated shows as masses of rounded granules. Each cell has a large 

 nucleus, .03 mm. in diameter, with a spheroidal nucleolus, .01 mm. in diameter. 



