ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 743 



Germinal Layers of Planarians.* — -Professor E. Selenka's commu- 

 nication to the Society of Erlangen is here abstracted ; he finds that in 

 Eurijlepta cristata the ova are only fertilized after deposition, and he 

 notes that only one spermatozoon enters the egg ; the blastopore 

 appears at the vegetative pole. The first tu-o blastomeres are gene- 

 rally of a difterent size ; their appearance is followed by that of two 

 small cells, and then it is seen that the largest blastomere is dorsal, 

 the next largest ventral, and that the two smallest respectively occupy 

 the right and left sides. At the anterior pole four small ectodermal 

 cells appear, and four formative cells lie below these; they give rise 

 to four small mesodermal cells, which are the seat of origin of the 

 muscles and of the reticulum, and so, therefore, of the tissue which 

 surroimds the ramifying branches of the enteron. At the posterior 

 pole there are seen four very small endodermal cells, which form the 

 proboscis ; a diagram is given in illustration of the topogi'aphy of these 

 parts. The author would seem to have found that the blastopore is 

 persistent, and that it forms the permanent mouth. The gastrula is 

 formed by ejjiboly. 



Leptoplana tremeUaris differs in having the blastomeres of the first 

 and second orders equal to one another in size, as well as by the fact 

 that there is no metamorphosis dui'ing the coui'se of development. 



Echinodermata. 



EcMnodermata of the Giilf of Triest.j — In giving a list of these 

 forms. Dr. E. Graeffe adds notes on the places in which they are to be 

 found, and as to the season of reproduction. He points out that 

 the develojjing forms have many enemies, whereas, so far as he knows, 

 the adults have none ; and he reminds us that large forms at any rate 

 have a peculiarly disagreeable smell, which would aid them, in addition 

 to their spines ; he says that it is rare to find Echinoderm-remains in 

 the stomachs of predatory fish. This circumstance would explain the 

 absence of any characters which could be referred to mimicry, and the 

 possession of the peculiarly bright coloration which they so 

 frequently exhibit. In some notes on their development he states 

 that in the first half of the year the Auricular} a-iovm predominates, 

 and in the second the Pluteus and Bipinnaria. No information could 

 be obtained as to the length of time necessary for the small non- 

 embryonic form to attain to its full size or to generative maturity. 

 As to their habits, we can only note that the sea-urchins cover them- 

 selves with algfe, shells, &c., and lie in wait for small fishes and 

 Crustacea. As is well known, the starfishes are fondest of Mollusca. 



Revision of the Holothnroida.i — Dr. H. Ludwig gives a revision 

 of the species of Holothurians collected by H. Mortens and described 

 by J. F. Brandt. He sinks the genera Oncinolabes, Liosonia, and 

 AspidocJiir. and the family Oncinolabidie formed by Semper later on. 

 He finds that of the twenty-three species described only six have not 



* Bull. Sci. Dep. Nord, iv. (1881) pp. 165-9. 



t Claus' Arbeiten, iii. (1881) pp. 333-14. 



J Zeitschr. f. wiss. Zoo!,, xssv. (1881) pp. 575-99. 



