THE BNTEROPNBUSTA. 39 



does not stain. These cells ai'e sufficiently represented in figs. 

 72 and 73a, which are, however, from B. minutus. In parts 

 of the skin which are of this kind the long cells of the ecto- 

 derm are comparatively few in number, and thus the skin has 

 a spongy consistency which is very characteristic. This is 

 true of the skin behind the collar in B. minutus, B. sal- 

 moneus, and B. Robinii. There is a general similarity 

 between the skins of all these forms, and probably their struc- 

 ture is the same as in B. Robinii. This statement, however, 

 only rests on the evidence of sections, as no teased preparations 

 were made of B. minutus. In the skin of the collar and 

 proboscis especially a small number of nuclei may be seen in 

 the higher layers of the skin. Whether these belong to young 

 cells of the tailed series or of the secreting type was not deter- 

 mined. Another set of small, generally bilid secreting cells, 

 are found in the proboscis skin ; the contents of these cells are 

 granular. 



There is one other point of importance in treating of the 

 skins of these forms, viz. the constant presence in teased pre- 

 parations of large spindle-shaped cells (fig. 77, c). As the 

 result of many observations it appeared nearly certain that 

 these had really been broken off from the ends of the long 

 ectoderm cells. Unless care was taken in the preparation this 

 frequently happened, many of the ectoderm cells being broken 

 and therefore without nuclei, and hence the probability that 

 this was the origin of the spindle-shaped cells. Since these 

 fusiform cells are generally most abundant at that level of the 

 skin at which the nuclei of the long cells are placed, the 

 appearance is suggested tliat they form a second layer of ecto- 

 derm cells ; but for the reasons above stated it seems likely that 

 this is erroneous, and that there is no such definite second layer. 



The resemblance between this skin and that of some 

 Nemertines, e.g. Mouopora vivipara (Salensky, ' Arch de 

 Biologic,' 1884), is very close. In this animal the same 

 spongy appearance is produced, and it is possible that the 

 deeper layer of ectoderm may be capable of the same expla- 

 nation. 



