INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 73 



by the author. The structural characters point to A. aquaticus as the 

 ancestor, but at present the districts occupied by the two forms have not 

 been shown to couamunicate. A descent from an extinct form is impro- 

 bable, as it demands a strain upon the laws of heredity or atavism to 

 account for the occurrence of the few specimens with eyes. It is easier 

 to conceive of a connection with A. cavaticus, an inhabitant of neigh- 

 bouring wells and pools, and of a transference of the species either from 

 these to the lake, with accompanying structural modifications, or vice 

 versa. The differences in structure already mentioned seem to justify 

 its separation from A. cavaticus as a distinct species peculiar to the 

 deep region of the lake. 



Anatomy of the Amphipoda.* — Professor Wrzesniowski, of War- 

 saw, deals in detail with the anatomy of Goplana polonica, Pallasea 

 cancellus, <ind two varieties of Gammarus pulex. 



In the first-mentioned form the hypodermis and the fatty body aro 

 both made up of small polygonal cells, which are provided with 

 nuclei and nucleoli, and are not separated from one another by any 

 intercellular substance. That their structure is not essentially the 

 same is shown by what obtains in Pallasea cancellus, for in this form 

 the hypodermis consists of a layer of typically arranged cylindrical 

 epithelial, while the fatty body is made uj} of larger, rounded, or 

 angular cells ; the former belongs to the series of epidermal and the 

 latter to the series of connective-tissue formations. The fatty body 

 is described as enveloping the entire tract, and as, while filling up 

 the interspace between it and the heart, forming a serous investment 

 for the latter ; this fatty body is, moreover, continued on to various 

 other organs, which it connects with one another and with the body- 

 wall. It is of interest to note that the first joint of the lower antennje 

 appears to be completely filled up by it ; and on either side of the 

 enteric tract it forms regions to which Weissman gave the name of 

 plates {Lcftodora hjalina). In starving amphipods, the fatty body 

 disappears almost completely. 



The flexor muscles of the trunk consist of two series ; of these, one 

 is directed forwards and downwards, and is to be found in each of the 

 segments from the fifth to the tenth. In tlie last three segments there 

 is a common flexor, and in the more anterior this system appears to be 

 completely absent. The other series is made up of longitudinal bands, 

 which form two layers on either side, and pass from one segment to the 

 next succeeding ; they arc found in the venti'al region, and have a direc- 

 tion parallel to the ventral surface. This system of " longitudinal " 

 muscles is regularly disposed from the fcnirth to the ninth segment. 

 In the tenth the ujiper layer is alone found, and, as before, there is 

 a fused muscle for the last three somites. The extensor muscles form 

 strong bands on either side, which are better developed than are the 

 flexors. The abdominal appendages aro moved by a com2)licated 

 system of muscles ; the first, or basal, joint has a flexor and an 

 extensor, which are capable of moving the whole foot backwards and 

 forwards, while the two terminal branches have also their special 

 musclet!. 



* 'Zool. Anzeigtr,' ii. (187U) pp. 117, 105. 



