Blood-corpuscles o/'Tridacna. 451 



reaction of the contained granules with osraic acid and basic 

 colouring-matters agreed exactly in the two kinds of cells. 

 In the Pulmonata also no evidence of glycogen was adduced, 

 but that we have to do with glycogen or a similar body is 

 at least probable since we know from Barfurth * that in the 

 Pulmonata glycogen is at times accumulated in great quantity 

 in the plasma-cells or Leydigian cells of the interstitial 

 connective substance. 



The much-discussed question of the intercellular spaces of 

 the epithelium of the Mollusca has now, we believe, found 

 its definitive solution in the recently published memoir by 

 Schiemenz f. The intercellular spaces are not artificially 

 produced, although their supposed stomata may be ; they do 

 not reach the surface of the epithelium, but terminate crecally 

 in sharp points between the epithelial cells. Although the 

 existence of intercellular spaces has been placed beyond a 

 doubt by means of injections (Schiemenz, Nalepa) and by the 

 observation of fresh objects (Leydig &c.)j the question 

 deserved consideration how far intercellular spaces may be 

 artificially produced by reagents causing hardening and 

 shrivelling. Schiemenz has already raised this question when 

 he brought forward this very objection to my observations of 

 intercellular spaces in the epithelium of the pedal glands of 

 the Pulmonata ^. In this particular case Schiemenz's scruples 

 were unfounded, for no one will doubt that intercellular spaces 

 which regularly function as the efferent ducts of glands, and 

 are often found tilled with the secretion of the glands, are 

 formed during life §. But as to the matter itself he is un- 

 doubtedly in the right. Of my three Tridacnce the osmium 

 and chromic-acid specimens showed a densely closed palis- 

 sade-epithelium without the smallest interstices between the 

 individual cells, while the spirit-specimen has the whole 

 epithelium traversed by numerous large typical intercellular 

 spaces. Only one of the two can represent the natural con- 



* Barfurtli, loc. cit, pp. 325 et seqq, 



t Paulus Schiemenz, *' Ueber die Wasseraufnahme bei Lamellibran- 

 cbiaten imd Gastropoden," 11., in Mitth. Zool. Stat. Neapel, Bd. vii. 

 Heft 3. 



X Schiemenz, loc. cit. p. 428. 



§ Although I have in the same place adduced the intercellular spaces 

 of the epithelium of the pedal glands as evidence for the existence of such 

 formations in general, this can no longer apply now that we know the 

 true nature of the permanently closed typical intercellular passages. The 

 two are quite different things, which must be kept apart. 



