REPORT ON THE NEMERTEA. 69 



Here, again, its generally homogeneous character, with the addition of the same 

 cellular and fibrous inclusions (intermediate stages between the two being similarly 

 rejaresented) as were noticed above, gives it an aspect similar to the corresponding tissue 

 in the other groups of Nemertea. 



It cannot be denied, and has been already noticed above, that from a morphological 

 point of view there are certain strong points of resemblance between the gelatinous tissue 

 of the Nemertea and the jelly of the Medusas. I was very desirous to know whether this 

 would also apply to the chemical constitution, and owing to Professor Krukenberg's kind 

 aid I am now able to make definite statements on this head. Having sent him a small 

 quantity of the Nemertean jelly, he kindly examined it and writes as follows : — 



" In accordance with your desire I have attempted, as far as it is possible, chemi- 

 cally to solve the question, whether the jelly of the Nemertea is more closely allied to 

 that of the Medusae or to the collagenous substances, such as I have with certainty 

 demonstrated in Sipunculus nudus (Vergl. physiol. Studien., i. 1882). As collagenous 

 tissue is digested by trypsine, only in case of its having before been treated with acids 

 or been boiled with water (Ewald and Kiihne), I tested the reaction of the Nemertean 

 jelly towards this ferment. It proved to be very easily digested by trypsine, and would 

 thus have to be regarded as a true proteid substance. Wholly in accordance with this 

 result is the intense red colour which the tissue acquires when boiled with Millon's 

 reagent ; whereas, on the contrary, tissues that contain more collagen are only faintly 

 stained, and pure collagen is not stained at all by Millon's reagent. Moreover, the 

 Nemertean jelly is not acted ujjon as are the collagens {' leimgebendes Gewebe') by 

 boiling water, nor does it furnish, when treated with diluted acids and soda, such reducing 

 solutions as are the so-called mucins (Hyalogene, mihi). The Medusa-jelly consists of true 

 proteid bodies.^ A similar substance is the vitreous body of the eye of vertebrates, and 

 I am thus fully prepared, after the experimental results obtained, to agree with you in 

 regarding the Nemertean jelly as an analogous product to the jelly of the Medusae, and 

 similarly of an albuminoid nature." 



We now pass to a discussion of the muscular layers. We will first discuss the general 

 distribution of muscular tissue, and reserve histological remarks for the conclusion. 



In discussing the muscular layers of the body-wall of the Nemertea, considerable 

 confusion still obtains in the writings of most of the older authors, and I must confess 

 that it took me a long time to see my way to a safe basis of comjjarison of the layers, 

 that may sometimes be only one, sometimes no less than five in number, three or two 

 being also very common occurrences. An outline of the homologies of the muscular layers 

 was given by myself in the article Nemertea in the recent edition of the Encyclopaedia 

 Britannica, and in the views there propounded I have no changes to make, only certain 

 further additions have been rendered possible by the aid of the Challenger material. 



1 Krukenberg, Vergl. pLysioL Studien., ii., 1 Abth., pp. 23-34. 



