358 LOUIS MAX HICKERNELL. 



and descriptions are therefore presented here for the first time. 



The finer cytological changes accompanying the process of 

 desiccation and subsequent recovery can only be shown after 

 describing the conditions present in a normal, undried specimen. 

 I shall therefore now describe the arrangement of organs and 

 their cytological peculiarities in both extended and contracted 

 normal animals, after which comparisons will be made with 

 sections of animals which have been desiccated and also with 

 sections of animals recovering from desiccation. 



A. The Normal Extended Animal. The relationship of the 

 internal organs is well shown in transverse sections of the ex- 

 tended Philodina. Fig. 7, Plate III., shows a section through 

 the posterior part of the head. The pharyngeal cavity leading 

 to the mastax is lined with cilia. Its wall consists of thick cells 

 with large nuclei. The brain, with outer cellular elements and 

 inner homogeneous zone, appears close to the pharyngeal tube. 

 The integument surrounding the region of this section is much 

 thinner than it is in the mid-body region. This is to be expected 

 when one remembers the flexibility of the head segments as 

 compared with those of the trunk. There is a marked similarity 

 in the arrangement of the elements here described and those in a 

 transverse section through the anterior part of Discopus synaptce 

 as described by Zelinka ('88). 



In Discopus, Zelinka shows the integument as being much 

 thinner than I have found it in Philodina. The hypodermis of 

 Philodina appears as a definite layer much thicker than the 

 cuticle and containing nuclei embedded in its syncytial ground- 

 work. This feature is seen in the figures of the sections through- 

 out all parts of the animal's body. In Discopus the nuclei are 

 flattened rather than round and appear as swellings upon the 

 cuticle. Furthermore, Zelinka figures the hypodermal nuclei 

 as being without a nucleolus. Such a condition is not usually 

 found in Philodina. Another point of variance between the two 

 forms concerns the brain. Zelinka figures the brain of Discopus 

 as being composed of an outer ganglionic layer and a central 

 "punktsubstanz." In Philodina the same divisions appear but 

 the cells of the ganglionic layer have distinct walls as distinguished 

 from the syncytial condition in the brain of Discopus. The 



