— 23 — 



Ärmadillidiuni granulatum Brandt. 



I have compared alcoliolic specimens of this species, collected by Dr. zur Strassen in 

 Dalmatia, with the preceding species in respect to tlie external form and structure of the first 

 two pairs of outer gills. I find that they correspond in all respects, differing only as regards com- 

 parative size and form. 



Ligidium Hypnorum Buddk-Lund. 



In this species the outer gills have no special modifications of structure in adaptation to 

 the respiration of air. In general they resemble in structure the last three pairs of outer gills in 

 PorceUio scaber. 



External Äppearance and Structure. Fig. 9 shows the appearance of the right 

 outer gill of the first pair, as viewed on the inner or dorsal sm-face. It is seen to he of a general 

 quadrilateral shape and is broader than long. The attachment with the basal Joint is at the 

 outer anterior corner of the gill. The face of the gill is dotted and the dots are so arranged as 

 to leave open Spaces. These are paths for the flow of the blood through the gül. The incurrent 

 path or Channel — beginning at the union of the gill with the basal Joint — extends laterally 

 across the gill and gives off branches toward the middle region of the gill. Here the branches 

 become lost in the small ü-regular Spaces lying among the dots. The excurrent path or Channel 

 lies along the posterior and outer margin of the gill. It has no branches but is in free communi- 

 cation with the spaces in which the branches of the incurrent Channel terminate. 



Examining the gill under higher magnification it is seen that the dots are nuclei, lying 

 immediately within the chitine and belonging (as further shown by the study of sections) to the 

 hypoderm. By focussing at different levels it may be seen that associated with many of the nuclei 

 are Strands of tissue which ruu from the upper to the lower layer of hypoderm. These form 

 supporting columns or pillars, such as have already been described for PorceUio scaher. It is due 

 to the grouping of these pillars that spaces and Channels for the passage of the blood through the 

 gill, as above described, are formed. Along the Channels the pillars tend to be arranged in rows, 

 forming a kind of broken wall to the channel. Elsewhere they are scattered and stand either singly 

 or in irregulär groups. 



Internal structure. Fig. 10 represents a cross-section of the outer gill, taken in the 

 direction of the line 55', Fig. 9. It is seen that the gill is in principle a simple sac containing 

 blood. The outer layer of the wall, composed of chitine, is mach thicker on the ventral than ou 

 the dorsal side of the gül. The hypoderm everywhere liues the chitine and in general varies with 

 it in thickness. It is very thin on the dorsal side and its nuclei for the most part lie in the 

 extensions of the hypoderm forming the pillars. The blood-cavity is everywhere bounded by a very 

 thin wall in which at distant intervals elongated nuclei occur. From its relations I infer that this 

 layer is mesodermic in origin. ' 



Function of the outer Gills. The structure of the gill as above described appears 



* See Foot-note, p. 14. 



