E. MAESHALLI. — YOUNG SPECIMENS. lOo 



A very important feature in all the little specimens under 

 consideration is the total absence of parietal oscula. These are 

 at any rate macroscopically still unopened. However, it can 

 easily be demonstrated under the microscope that there exist in 

 tiie wall, especially at the bulged middle portion of the body, 

 certain canals or niches which, like the typical excurrent canals, 

 extend \Yith a free lumeu from the gastral cavity, but, which 

 unlike them, are not blindly capped by the chamber-layer at 

 the outer end. There is, at the spots in question, a gap in 

 the chamber-layer and here the gastral cavity stands in fiee 

 communication with the outer world through the narrow lacunce 

 between the trabecula?. At the spots a condition obtains quite 

 similar to that iigured bv F. E. Schulze in the Challenger- 

 Eeport ('87, Pi. LTII, fig. o) for young Lanuginella impa at the 

 part where the oscular area should later develop itself. I suppose 

 that functionally the S2)0ts in the above described condition are 

 already playing the role of j^arietal oscula. The latter will become 

 definitely established, if only the trabecule and the dermal 

 skeleton give way for a fieer passage than before, in order to 

 meet the requirement of an ever increasing quantity of outflowing 

 water. I find the above idea concerning the formation of parietal 

 oscula perfectly corroborated l)y my observations on the growing 

 parts of larger specimens. 



The character of the wall in quite young Euphctella might 

 then be said to agree essentially with that of Hohscus (see p. 39). 

 The only important difference between the two genera mentioned 

 seems to consist in tlie development or non-development of parietal 

 oscula. The well-developed external ledges of Euplectella, as also 

 of RegadreU((, are apparently the outcome of the excessive 



