of invertebrate groups just for the sake of clearing questions 

 of mammalian physiology, is wrong to my opinion. The many 

 errors in his work will be discussed in various chapters, it is 

 of no use to discuss them here. 



These examples may serve to show the desirability of a 

 careful re-testing of all the work of older investigators. Many 

 mistakes have passed unnoticed and came into the text-books. 



A summary of the literature which generally appears in the 

 beginning of a somewhat larger paper like the present one, 

 will not be given in this introduction, because there is practi- 

 cally no important literature and because the data which can 

 be found scattered in the different journals, have been summa- 

 rised in an excellent way by Biedermann in Winter- 

 stein's Handbuch 135) and by Jordan in the first part of 

 his: Vergleichende Physiologie 142). 



The writer does not flatter himself to have collected the 

 whole literature and to some important papers little attention 

 has been paid. This was necessitated by his desire not to drown 

 the personal observations in the immense literature. 



The groups of the Crinoids and the Ophiurids have been left 

 out for practical reasons, because no appropriate'material could 

 be obtained. 



2. SPECIES USED. 



As a representative of the group of the Asteroidea I have 

 used Asterias Forbesii (Desor) Verrill, a starfish, very common 

 around W o o d s H o 1 e. It is as far as appearance is concerned, 

 practically identical with our A. vulgaris, but for the madre- 

 poric plate which is more clearly visible in the American 

 species by its brilliant orange color. 



The sea-urchin which I used, Arbacia punctulata (Lm.) Gray, 

 is also very common in the neighbourhood of Woods Hole. 

 It is a rather small form of a dark violet color with long 

 spines. Its shell is semi-spherical in form, rather thick and 

 provided with a so-called epistroma. The periproct is oval, the 

 place of opening of the anus, covered by numerous sceletal 

 elements in other urchins, is in the family of the Arbaciidae 

 covered with four triangular plates. The interradia are open 

 in the neighbourhood of the apex. 



The spines are flattened — in the way of a spatula — on 

 one side at their top. The tuberculae are not perforated, secon- 

 dary tuberculae are not present. 



Thyone briareus. Lesueur (= Anaperus br. Pourtales ^= 

 Sclerodactyla br. Ayres, Verrill) is the dendrochirote Holo- 

 thurian, which I studied in Woods Hole. It is dark brown- 

 greenish in color, almost black, ascidian-like ; its size depends 

 largely on the state of contraction of the musculature of the 



