42 



THE AMEEICAN MONTHLY 



[March, 



surface of the sphere. The dias- 

 tole is very slow (perhaps once in a 

 minute), but the systole is compa- 

 ratively active. These vacuoles may 

 be compared to the contractile 

 vesicles of the Infusoria. As con- 

 traction takes place, the pseudopo- 

 dia in the immediate neighborhood 

 of the vesicle, gently incline their 

 apices toward a certain point, with- 

 out in the slightest degree bending 

 their axes ; hence, if the vesicle 

 undergoing contraction be on the 

 surface of the animal opposite to 

 the observer, and thus hidden from 

 view, one may readily diagnose the 

 contraction. 



Concerning the nature of the 

 pseudopodia, which are complex in 

 their structure, there has been much 

 discussion by various observers. 

 When a pseudopodium is seen un- 

 der a high-power, two distinct ele- 

 ments may be distinguished entering 

 into its composition. In the centre 

 of the ray there is an axis-filament, 

 a thread-like structure, which is 

 supposed to afford support to the 

 protoplasm which surrounds it. It 

 is about the nature of this axis that 

 learned men have so much differed. 

 Greeff and Eilhard Schulze concur 

 in regarding it as a cylindrical 

 spine, skeletal in nature and im- 

 port, perhaps consisting of siliceous 

 material, and they maintain that it 

 penetrates the endosarc. On the 

 other hand, Max Schulze, Hertwig 

 and Lesser, and Archer, regard the 

 axis as a peculiar form of contrac- 

 tile plasma, possessing more or less 

 rigidity, and not as a spine. Schulze 

 and Archer aver that it only reaches 

 to and rests upon the endosarc ; 

 these are matters that are well 

 worthy of further research. 



Two axes have been observed in 

 one pseudopodium — an evidence 

 that two rays have united. The 

 pseudopodia may unite, or anasto- 

 mose, but they never branch. 



Several individuals have been seen 

 to unite to form one body ; in these 

 instances the nuclei of the various 

 individuals remained distinct ; more- 

 over, the animals may be artificially 

 separated. 



As to the manner of taking food, 

 these creatures, which are exceed- 

 ingly slow in locomotion, rest quietly 

 with the pseudopodia extended, and 

 wait for the food to come to them, 

 and an infusorian animalcule or a 

 rotifer by merely swimming against 

 a ray, adheres to it, and this ray 

 will immediately begin to retract, 

 other rays will come to its assistance, 

 and by the time the victim is drawn 

 down to the surface of the body, it 

 is almost entirely encysted in pro- 

 toplasm. While passing through 

 the ectosarc, it becomes completely 

 encased, and if the creature be a 

 rotifer, or an animal of considerable 

 vitality, it may continue its strug- 

 gles to free itself until it has fully 

 passed into the medullary portion, 

 where it is digested and assimilated. 

 All the pseudoj)odia near the point 

 of entrance into the sphere, are 

 partially withdrawn and are much 

 inclined toward this point ; the 

 ectosarc at this place becomes much 

 depressed, and considerable time 

 will elapse before the body will 

 assume the spherical form again, 

 and the pseudopodia be extended. 



It is quite apparent to my mind, 

 that the axes of these rays, do not 

 consist of a calcareous, silicious, or 

 hard tissue of any kind ; it is quite 

 in accordance with what we observe 

 in the movements of the pseudopo- 

 dia, to regard the axes as being 

 composed solely of a dense, com- 

 pact protoplasm ; so far as I know, 

 no movement of the sarcode-sub- 

 stance has been noticed in the axes, 

 but there is a slow, continuous cir- 

 culation of the protoplasm in which 

 they are imbedded, and in fact this 

 slow movement takes place in other 



