260 Prof. P. M. Duncau on the Genus Hindia. 



In the presence of such contradictory opinions, all of which, 

 without exception, have very slight foundation in fact, it cer- 

 tainly seems best at present to keep silence. According to 

 most authors the " endoderm " and " ectoderm," whatever 

 may be their distribution in the body, furnish only the epi- 

 thelia. All the rest — genital products, skeletal system, in 

 general the body proper — is formed from " mesoderm." Every 

 spongologist will doubtless, then, be somewhat startled to 

 learn from Kleinenberg * that there is generally no mesoderm 

 present. 



We may shortly sum up our results in the following sen- 

 tences : — 



1. The Sponges must not be classed amongst the Coelen- 

 terata. They form a type of their own, 



2. The Sponges are probably descended from free-swim- 

 ing forms, which, originally without supporting structures, 

 ultimately developed a strong skeleton. 



3. These primitive forms lived at great depths. 



4. Goincidently with life at less depths degeneration of 

 the (siliceous) skeleton took place. 



XXXII. — A Reply to Dr. O. J. Hindis Communication "On 

 the Genius Hindia, Dune, and the Name of its Typical 

 Species^ By Prof. P. Martin Duncan. 



Aftee a careful study of Dr. Hinde's paper (Ann. & Mag. 

 Nat. Hist. Jan. 1887, p. 67) 1 ^nd that it adds very little to 

 our previous knowledge of the interesting Silurian sponge. 

 It is important that the geographical range of the form should 

 have been increased, and it is exceedingly satisfactory that 

 Dr. Hinde should have been able to find some siliceous spicules 

 the shape of which corroborates the statement made by me 

 that the form resembled a tetraclade lithistid. Tlie bulk of the 

 paper consists of criticisms, partly self-contradictory, however, 

 and unsatisfactory in their tone, and partly useful in re- 

 exposing possible errors which had already been discovered 

 by Dr. liauff. 



Dr. Hinde endeavours to explain the strong contradiction 

 regarding the value of Eoemer's specific diagnosis by asserting 

 that the casts described by that author are recognizable as 

 the casts of the species H. Jibrosa = H. sphceroidalis, nob. 



* Zeitscbr. fiir wiss. Zool. Bd. xliv. 



