23 
Armadillidium granulatum Brandt. 
I have compared alcoholic specimens of this species, collected l)y Dr. zur Strassen in 
Dalmatia, with the preceding species in respect to the external form and structure of the first 
two pairs of outer gills. I find that they correspond in all respects, difi’ei’ing only as regards com- 
parative size and form. 
Ligidium Hgpnorum Budde-Lund. 
In tliis 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 scaher. 
External Appearance and Structure. Fig. 9 shows the appearance of the right 
outer gill of the first pair, as viewed on the inner or dorsal surface. It is seen to be 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 gill. The incurrent 
l^ath 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 irregular spaces lying among the dots. The excurrent path or channel 
lies along the ijosterior and outer margin of the gill. It has no branches l)ut 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 l)elonging (as further shown by the study of sections) to the 
hypoderm. By focussing at different levels it may he seen that associated with many of the nuclei 
are strands of tissue which run 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 tlie 
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 irregular groups. 
Internal structure. Fig. 10 represents a cross-section of the outer gill, taken in the 
du’ection 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 much thicker on the ventral than on 
the dorsal side of the gill. The hypoderm everywhere lines the chitine and in general varies witli 
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 tlie gill as above described appears 
See Foot-note, p. 14. 
