110 Mr. H. J. Carter on Spermatozoa in the Spongida. 



measure more than 15-6000ths of an inch in diameter, it would 

 seem that there is a difference in size, if not in development, 

 between the ovum of the siliceous and calcareous sponges, 

 when sufficiently matured to leave the parent. 



From this I almost question whether the ovum in the sili- 

 ceous sponges does not leave the parent before it arrives at the 

 Gastrula state — that is, in the state of the Planula, when the 

 cavity of the endoderm does not communicate with the exterior, 

 but when the ciliated cells of the ectoderm are sufficiently 

 developed to give the ovum full power of locomotion. This, 

 however, is for future observation to determine. One point is 

 evident, viz. that in the siliceous sponges the spicules are 

 plentifully developed before the ovum leaves the parent, which 

 is not the case with the Gastrula in the calcareous sponges, so 

 far as my observation extends. 



Since the above was written, I have obtained specimens of 

 Grantia ciliata, Johnston (Sycandra, H.), in the oviparous 

 state, but have not been able to detect any thing like sperma- 

 tozoa in them. Indeed, only in the instances above mentioned 

 have I ever met with any thing like spermatozoa, although I 

 have examined living sponges hundreds of times under the 

 microscope. Still I am well aware, from long experience, 

 that, among the lower organisms, the meeting with the sper- 

 matic element is a matter of chance rather than of certainty. 



EXPLANATION OF PLATE X. 



N.B. — All the figures in this Plate, from 1 to 16 inclusive, have been 

 taken from a piece of Esperia cegagropila, Carter (Halichondria agagro- 

 pila, Johnston, Brit. Sponges, p. 119, and type specimen, Johnstonian 

 collection, British Museum). They also have all been drawn to the 

 scale of l-12th to 1 -6000th of an inch (with the exception of 13, c, and 

 16, a), in order that their relative sizes may be at once appreciated. Of 

 course the finer lines are diagrammatic. 



Fig. 1. Transparent, empty, distended globular cell : a, cell-wall ; b, 



nucleus or cytoblast. 

 Fig. 2. Granuliferous nucleus or cytoblast (undistended?). 

 Fig. 3. Tricurvate spicule, full-grown. 

 Fig. 4. Mother cell of tricurvate spicule. The young tricurvates in 



plurality arranged parallel to each other in a bundle, as they 



are wont to be in natural development : a, cell-wall ; b, nucleus ; 



c, tricurvates. 

 Figs. 5 & 6. The same, but with some of the tricurvates reversed. 

 Fig. 7. The same, where the tricurvates cross each other at nearly right 



angles. 

 Fig. 8. The same as figs. 5 and 6, but at an earlier stage of development, 



therefore smaller. 

 Fig. 9. The same, and the smallest size recognized, being not more than 



1 -3000th of an inch in longest diameter. 

 Fig. 10. Bihamate spicule, full-grown. 



