30 
ORGANIC DEPENDENCE AND DISEASE 
and clam. Tlie rest are free (gastropods 39, pteropods 
32 species). The sponges of the Cambrian are as yet in a 
large measure undescribed but the material in the collec- 
tions made by Dr. Walcott from the Burgess shale indicates 
the great abundance of the silicious sponges, while they re- 
tain a simplicity of form which is in contrast to the pro- 
gressed species of the Devonian. 
With the foregoing we may contrast the great outstand- 
ing army of independents — the Crustacea. Of the trilo- 
bites there are 502 species and of the Encrnstacea, the prim- 
itive shrimps, 89 species — together constituting one-lialf 
the entire list of described species of the fauna. These 
creatures were all elaborately innervated and highly loco- 
motive throughout their entire life, and their anatomical 
and functional structure was a very advanced attainment 
in specialization. Such an enormous development of the 
single type of structure represented by the trilobites, which 
were here at the climax of their entire career on earth, gave 
material and opportunity for different degrees of progress, 
delay, decline and reversion, all of which are to be estimated 
in the construction of a true classification of the great 
group. No adequate conception of their specialization can 
be obtained without a study of the restorations of their ven- 
tral anatomy as shown by Neolenus, a late member of this 
Cambrian or “ first fauna.” This has been restored by 
C. D. Walcott on the basis of specimens collected by him in 
the Middle Cambrian of Burgess Pass, Alberta. The trilo- 
bite has maintained throughout its individual (ontogenic) 
and race (pliylogenic) existence, complete freedom and full 
locomotor efficiency. And if this is true of them it is a 
fortiori true of the Eucrustacea 1 of this fauna of which 
i These Eucrustacea are creatures which to the casual observer show evident 
relationship to the ‘ ‘ shrimps. ’ ’ It is interesting to a paleontologist to observe 
the unconscious solemnity w 7 ith which biologists familiar alone with evident 
structures in the vast group of living arthropods or jointed invertebrates, and 
their classification, debate with themselves the position and affinities of these 
