6 NATURAL HISTORY BULLETIN. 



The Nematophores. There is a great deal of confusion of 

 terms regarding these structures. The name properly applies 

 to both the sarcodal process and the chitinous receptacle into 

 which it retracts, although it is often used to denote either one 

 of these structures. The terms "sarcostyle," denoting the sar- 

 codal process, and "sarcotheca," denoting the chitinous recep- 

 tacle, have now come into general use. Hincks' description 

 of P. -pinnata is incomplete, in that it does not notice the sar- 

 costyles which occur without the investing sarcothecEe. One 

 pair of these naked sarcostyles is found in the usual position 

 of the supracalycine nematophores, and another pair is in the 

 axil of each hydrocladium. 



The structure of the nematophores has been the subject of 

 much discussion, particularly by Hincks, Allman, Reichart, 

 Merejkowsky, Weismann, and Jickeli. With the excellent 

 facilities afforded by the Plymouth laboratory, and the valu- 

 able suggestions of its director, I secured a number of fortu- 

 nate serial sections of the expanded sarcostyles of P. pinnata, 

 and have been able to satisfy myself concerning the main points 

 of their structure. The results of this study have corrobo- 

 rated the statements of Merejkowsky up to a certain point, 

 including the following facts — 



i. The greater part of the sarcostyle is composed of 

 ectodermal cells. 



2. There is a central endoderm core (or cylinder?) 1 



3. The cells on one side of this core are very large and 

 quadrangular, while the cells on the other side and of the 

 entire terminal portion of the sarcostyle are of ordinary size. 



4. There are pseudopodia-like processes from the free sur- 

 face of the sarcostyle. 



On the other hand, I have been entirely unable to find any trace 

 of the "interstitial protoplasm" described by Merejkowsky, in 

 which he claims that the ectodermal cells are imbedded. 

 Weismann 3 boldly suggests that this "interstitial protoplasm" 



1 While at Naples, the writer was able to demonstrate that this structure, 

 in another species, has a central cavity. 



8 Die Entstehung der Sexualzellen bei den Hydroniedusen, p. 176. 



